ARM / OMAP: Use struct syscore_ops for "core" power management

Replace the sysdev class and struct sys_device used for power
management in the OMAP's GPIO code with a struct syscore_ops object
which is simpler.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Kevin Hilman <khilman@ti.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>