allwinner: Always use a 3MHz RSB bus clock
allwinner: Always use a 3MHz RSB bus clock

None of the other drivers (Linux, U-Boot, Crust) need to lower the bus
clock frequency to switch the PMIC to RSB mode. That logic is not needed
here, either. The hardware takes care of running this transaction at the
correct bus frequency.

Signed-off-by: Samuel Holland <c16aab9fe3288df0fb8fc1d24990a300b6b8f299@sholland.org>
Change-Id: Idcfe933df4da75d5fd5a4f3e362da40ac26bdad1

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware