x86/mce: Unify AMD DFR handler with MCA Polling

AMD systems optionally support a deferred error interrupt. The interrupt
should be used as another signal to trigger MCA polling. This is similar to
how other MCA interrupts are handled.

Deferred errors do not require any special handling related to the interrupt,
e.g. resetting or rearming the interrupt, etc.

However, Scalable MCA systems include a pair of registers, MCA_DESTAT and
MCA_DEADDR, that should be checked for valid errors. This check should be done
whenever MCA registers are polled. Currently, the deferred error interrupt
does this check, but the MCA polling function does not.

Call the MCA polling function when handling the deferred error interrupt. This
keeps all "polling" cases in a common function.

Add an SMCA status check helper. This will do the same status check and
register clearing that the interrupt handler has done. And it extends the
common polling flow to find AMD deferred errors.

Clear the MCA_DESTAT register at the end of the handler rather than the
beginning. This maintains the procedure that the 'status' register must be
cleared as the final step.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20251104-wip-mca-updates-v8-0-66c8eacf67b9@amd.com

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