zephyr/mpconfigport_minimal: Use MICROPY_CONFIG_ROM_LEVEL_MINIMUM.

This commit adjusts the configuration of the minimal zephyr build to use
MICROPY_CONFIG_ROM_LEVEL_MINIMUM.  That's a lot cleaner than explicitly
enabling/disabling options.

Prior to this change the minimal build for qemu_cortex_m3 had size:

    Memory region         Used Size  Region Size  %age Used
               FLASH:      114436 B       256 KB     43.65%
                 RAM:       26320 B        64 KB     40.16%

and had the following test results (running using the CI settings, ie
`-d basics float --exclude inf_nan_arith`):

    352 tests performed (7092 individual testcases)
    352 tests passed
    254 tests skipped: ...

With the changes here the qemu_cortex_m3 size is now:

    Memory region         Used Size  Region Size  %age Used
               FLASH:       99428 B       256 KB     37.93%
                 RAM:       26312 B        64 KB     40.15%

That's a good decrease of about 15k firmware size.  And the test suite
still passes with:

    342 tests performed (6776 individual testcases)
    341 tests passed
    265 tests skipped: ...

Signed-off-by: Damien George <damien@micropython.org>

0 files changed, 0 insertions, 0 deletions