gpio/omap: remove bank->method & METHOD_* macros

The only bank->type (method) used in the OMAP GPIO driver is MPUIO type as they
need to be handled separately. Identify the same using a flag and remove all
METHOD_* macros.

mpuio_init() function is defined under #ifdefs. It is required only in case
of MPUIO bank type and only when PM operations are supported by it.
This is applicable only in case of OMAP16xx SoC's MPUIO GPIO bank type.
For all the other cases it is a dummy function. Hence clean up the same
and remove all the OMAP SoC specific #ifdefs.

Signed-off-by: Charulatha V <charu@ti.com>
Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>