Move the platform driver registration to a core_initcall, instead of an
arch_initcall.  This will allow us to use gpio related calls in
init_machine() (which is an arch_initcall) after adding the gpio
platform devices.

Cc: Alessandro Rubini <rubini@unipv.it>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>