ARM: ux500: Register the AB8500 from DB8500 MFD

As the AB8500 is a subordinate MFD device to the DB8500-PRCMU,
for consistency and a better 1:1 depiction of how the hardware
is laid out, it is a good idea to register it in the same way
as we do for the other MFD child devices. In order for us to do
this successfully we have to pass AB8500's platform data when
registering the DB8500-PRCMU from platform code.

Also solves this issue:
WARNING: at fs/sysfs/dir.c:526 sysfs_add_one+0x88/0xb0()
sysfs: cannot create duplicate filename '/bus/platform/devices/ab8500-core.0'

Reported-by: Linus Walleij <linus.walleij@linaro.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>