mmc: use an enumerated type to represent PARTITION_CONFIG fields

mmc: use an enumerated type to represent PARTITION_CONFIG fields

Modern eMMC v4+ devices have multiple hardware partitions per the JEDEC
specification described as:
  Boot Area Partition 1
  Boot Area Partition 2
  RPMB Partition
  General Purpose Partition 1
  General Purpose Partition 2
  General Purpose Partition 3
  General Purpose Partition 4
  User Data Area

These are referenced by fields in the PARTITION_CONFIG register
(Extended CSD Register 179) which is defined as:
bit 7: reserved
bit 6: BOOT_ACK
  0x0: No boot acknowledge sent (default
  0x1: Boot acknowledge sent during boot operation Bit
bit 5:3: BOOT_PARTITION_ENABLE
  0x0: Device not boot enabled (default)
  0x1: Boot Area partition 1 enabled for boot
  0x2: Boot Area partition 2 enabled for boot
  0x3-0x6: Reserved
  0x7: User area enabled for boot
bit 2:0 PARTITION_ACCESS
  0x0: No access to boot partition (default)
  0x1: Boot Area partition 1
  0x2: Boot Area partition 2
  0x3: Replay Protected Memory Block (RPMB)
  0x4: Access to General Purpose partition 1
  0x5: Access to General Purpose partition 2
  0x6: Access to General Purpose partition 3
  0x7: Access to General Purpose partition 4

Note that setting PARTITION_ACCESS to 0x0 results in selecting the User
Data Area partition.

You can see above that the two fields BOOT_PARTITION_ENABLE and
PARTITION_ACCESS do not use the same enumerated values.

U-Boot uses a set of macros to access fields of the PARTITION_CONFIG
register:

There are various places in U-Boot where the BOOT_PARTITION_ENABLE field
is accessed via EXT_CSD_EXTRACT_PARTITION_ACCESS and converted to a
hardware partition consistent with the definition of the
PARTITION_ACCESS field which is also the value used to specify the
hardware partition of the various mmc_switch incarnations.

To add some sanity to the distinction between BOOT_PARTITION_ENABLE
(used to specify the active device on power-cycle) and PARTITION_ACCESS
(used to switch between hardware partitions) create two enumerated types
and use them wherever struct mmc * part_config is used or the above
macros are used.

This represents no code changes.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>