fix(mmc): remove broken, unsecure, unused eMMC RPMB handling

Replay-protected memory block access is enabled by writing 0x3
to PARTITION_ACCESS (bit[2:0]). Instead the driver is using the
first boot partition, which does not provide any playback protection.
Additionally, it unconditionally activates the first boot partition,
potentially breaking boot for SoCs that consult boot partitions,
require boot ack or downgrading to an old bootloader if the first
partition happens to be the inactive one.

Also, neither enabling or disabling the RPMB observes the
PARTITION_SWITCH_TIME. As there are no in-tree users for these
functions, drop them for now until a properly functional implementation
is added. That one will likely share most code with the existing boot
partition switch, which doesn't suffer from the described issues.

Change-Id: Ia4a3f738f60a0dbcc33782f868cfbb1e1c5b664a
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>