mmc: allow use of hardware partition names for mmc partconf

mmc: allow use of hardware partition names for mmc partconf

eMMC v4+ devices have hardware partitions that are accessed via the
PARTITION_CONFIG (Extended CSD Register 179) PARTITION_ACCESS
and BOOT_PARTITION_ENABLE fields defined as:
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

Add char arrays to provide names for these values.

Use these names which displaying or setting the PARTITION_CONFIG
register via the 'mmc partconf' command.

Before:
u-boot=> mmc partconf 2 1 1 0 && mmc partconf 2
EXT_CSD[179], PARTITION_CONFIG:
BOOT_ACK: 0x1
BOOT_PARTITION_ENABLE: 0x2
PARTITION_ACCESS: 0x0

After:
u-boot=> mmc partconf 2 1 1 0 && mmc partconf 2
EXT_CSD[179], PARTITION_CONFIG:
BOOT_ACK: 0x1
BOOT_PARTITION_ENABLE: 0x1 (boot0)
PARTITION_ACCESS: 0x0 (user)
u-boot=> mmc partconf 2 1 boot1 0 && mmc partconf 2
EXT_CSD[179], PARTITION_CONFIG:
BOOT_ACK: 0x1
BOOT_PARTITION_ENABLE: 0x2 (boot1)
PARTITION_ACCESS: 0x0 (user)

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