This sub-command adds support for the RPMB partition of an eMMC:
* mmc rpmb key <address of the authentication key>
  Programs the authentication key in the eMMC This key can not
  be overwritten.
* mmc rpmb read <address> <block> <#count> [address of key]
  Reads <#count> blocks of 256 bytes in the RPMB partition
  beginning at block number <block>. If the optionnal
  address of the authentication key is provided, the
  Message Authentication Code (MAC) is verified on each
  block.
* mmc rpmb write <address> <block> <#count> <address of key>
  Writes <#count> blocks of 256 bytes in the RPMB partition
  beginning at block number <block>. The datas are signed
  with the key provided.
* mmc rpmb counter
  Returns the 'Write counter' of the RPMB partition.

The sub-command is conditional on compilation flag CONFIG_SUPPORT_EMMC_RPMB

Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Pierre Aubert <p.aubert@staubli.com>
CC: Wolfgang Denk <wd@denx.de>