media: platform: s5p-g2d: move config to its own file

In order to better organize the platform/Kconfig, place
s5p-g2d-specific config stuff on a separate Kconfig file.

Acked-by: Łukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>