spmi: spmi-pmic-arb: add support to map SPMI addresses to physical addr

Add an exported function which can map an SPMI address to the
physical address range of the registers used to write to that
SPMI address.

The feature can be used by consumer drivers that need to lock
down access to certain PMIC peripherals temporarily for certain
secure use cases.

Change-Id: Ib477778346df29ee90661d2e07d2d3a5d160ae87
Signed-off-by: David Collins <collinsd@codeaurora.org>