MFD: mcp-sa11x0: move setup of PPC unit out of mcp-sa11x0.c

Patch taken from af9081ae (ARM: sa1100: Refactor mcp-sa11x0 to use
platform resources.) by Jochen Friedrich <jochen@scram.de>, and
consolidated to use a common function.

Move the setup of the PPC unit out of mcp-sa11x0 into the core SA11x0
code, and call it from each platforms initialization file.  This
centralizes the setup of the PPC unit while not polluting the mcp-sa11x0
driver with these details.

Acked-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>