media: platform: rename s5p-g2d/ to samsung/s5p-g2d/

As the end goal is to have platform drivers split by vendor,
rename s5p-g2d/ to samsung/s5p-g2d/.

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