refactor(mmc): replace magic value with new PART_CFG_BOOT_PARTITION_NO_ACCESS

Disabling access to the boot partition reverts the MMC to read from the
user area. Add a macro to make this clearer.

Suggested-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Change-Id: I34a5a987980bb4690d08d255f465b11a4697ed5a
2 files changed