[driver model] Rewrite system device API

System devices are special, and after two years of listening to Linus
preach this, it finally sunk in enough to do something about. We don't
need to regard them as real devices that reside on a peripheral bus and
can be dynamically bound to drivers. If we discover, e.g. a CPU, we know
by default that we have a driver for it, and we know damn well that we
have a CPU. We still need to keep track of all the devices, and all the
devices of a particular type. The kobject infrastructure allows us to do
this, without the overhead of the regular model.

A new subsystem is defined that registers as a child object of 
devices_subsys, giving us:

        /sys/devices/system/

struct sysdev_class {
        struct list_head        drivers;

        /* Default operations for these types of devices */
        int     (*shutdown)(struct sys_device *);
        int     (*suspend)(struct sys_device *, u32 state);
        int     (*resume)(struct sys_device *);
        struct kset             kset;
};

Defines a type of system device. These are registered on startup, by e.g. 
drivers/base/cpu.c. The methods are default operations for devices of that 
type that may or may not be used. For things like the i8259 controller, 
these will be filled in, since it is registered by the same component that 
the device controls reside in. 

For things like CPUs, generic code will register the class, but other 
architecture-specific or otherwise configurable drivers may register 
auxillary drivers, that look like: 

struct sysdev_driver {
        struct list_head        entry;
        int     (*add)(struct sys_device *);
        int     (*remove)(struct sys_device *);
        int     (*shutdown)(struct sys_device *);
        int     (*suspend)(struct sys_device *, u32 state);
        int     (*resume)(struct sys_device *);
};


Each auxillary driver gets called during each operation on a device of a 
particular class. 
Auxillary drivers may register with a NULL class parameter, in which case 
they will be added to a list of 'global drivers' that get called for each 
device of each class. 


Besides providing a decent of cleanup for system device drivers, this also 
allows:

- Special handling of system devices during power transitions. 

  We no longer have to worry about shutting down the PIC before we shut 
  down any devices. We can shut down the system devices after we've shut 
  down every other device. 

  Ditto for suspend/resume cycles. Almost (if not) all PM actions for 
  system devices happen with interrupts off, and require only one call, 
  which makes that easier. But, we can also make sure we take care of 
  these last during suspend and first during resume.

- Easy expression of configurable device-specific interfaces. 

  Namely cpufreq and mtrr. We don't have to worry about mispresentation in 
  the driver model (like recent MTRR patches) or using a cumbersome 
  interface ({device,class}_interface) that don't receive all the 
  necessary calls. 

- Consolidation of userspace representation.

  No longer do we have /sys/devices/sys, /sys/bus/sys, and /sys/class/cpu,
  etc. We have only /sys/devices/system: 

# tree /sys/devices/system/
/sys/devices/system/
|-- cpu
|   `-- cpu0
|-- i8259
|   `-- i82590
|-- lapic
|   `-- lapic0
|-- rtc
|   `-- rtc0
`-- timer
    `-- timer0

Each directory in 'system' is the class, and each directory under that is 
the instance of each device in that class. 

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