[media] s5p-mfc: Don't allocate codec buffers from pre-allocated region

Further investigation revealed that codec buffers also don't need to
be allocated at higher addresses than firmware base for MFC v6+ hardware.
Those buffers can be quite large and its size depends on the selected
format and framesize. This patch changes the way the codec buffers are
allocated - driver will use generic allocator for them instead of the
pre-allocated buffer for firmware and contexts.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>