ARM: 6336/1: U8500 PRCMU driver

Add an initial driver for communicating with the Power, Reset and
Clock Management Unit (PRCMU) firmware in U8500.
This initial version supports AB8500 communication only.

Signed-off-by: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
Signed-off-by: Mattias Wallin <mattias.wallin@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>