[media] Remove references to non-existent PLAT_S5P symbol

The PLAT_S5P Kconfig symbol was removed in commit d78c16cc
("ARM: SAMSUNG: Remove remaining legacy code"). However, there
are still some references to that symbol left, fix that by
substituting them with ARCH_S5PV210.

Fixes: d78c16cc ("ARM: SAMSUNG: Remove remaining legacy code")

Reported-by: Paul Bolle <pebolle@tiscali.nl>
Cc: <stable@vger.kernel.org> # for 3.17
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>