This can now be selected by setting MICROPY_HW_SDCARD_SDMMC, which defaults
to 1, ie SDMMC1. This commit also renames the SD pin configuration macros
from MICROPY_HW_SDMMC2_xxx to MICROPY_HW_SDCARD_xxx, as well as renaming
MICROPY_HW_SDMMC_BUS_WIDTH to MICROPY_HW_SDCARD_BUS_WIDTH.
Signed-off-by: Damien George <damien@micropython.org>