mtd: rawnand: omap_gpmc: Deprecate asm/arch/mem.h

We want to get rid of <asm/arch/mem.h> so don't
enforce it for new platforms.

This also means GPMC_MAX CS doesn't have to be defined
by platform code.

Define it locally here for now.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/all/20221011115012.6181-2-rogerq@kernel.org


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>