spl: mmc: get rid of emmc boot code duplication

spl: mmc: get rid of emmc boot code duplication

Get rid of emmc boot code duplication in spl_mmc_load_image() using a switch
case fallthrough into MMCSD_MODE_RAW. Since the #ifdef CONFIG_SUPPORT_EMMC_BOOT
check is not really necessary, remove it in the process.

No functional changes.

Signed-off-by: Nikita Kiryanov <[email protected]>
Cc: Igor Grinberg <[email protected]>
Cc: Paul Kocialkowski <[email protected]>
Cc: Pantelis Antoniou <[email protected]>
Cc: Tom Rini <[email protected]>
Cc: Simon Glass <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Tom Rini <[email protected]>