[media] s5p-mfc: Add support for probe-time preallocated block based allocator

Current MFC driver depends on the fact that when IOMMU is available, the
DMA-mapping framework and its IOMMU glue will use first-fit allocator.
This was true for ARM architecture, but its not for ARM64 arch. However, in
case of MFC v6+ hardware and latest firmware, it turned out that there is
no strict requirement for ALL buffers to be allocated on higher addresses
than the firmware base. This requirement is true only for the device and
per-context buffers. All video data buffers can be allocated anywhere for
all MFC v6+ versions.

Such relaxed requirements for the memory buffers can be easily fulfilled
by allocating firmware, device and per-context buffers from the probe-time
preallocated larger buffer. This patch adds support for it. This way the
driver finally works fine on ARM64 architecture. The size of the
preallocated buffer is 8 MiB, what is enough for three instances H264
decoders or encoders (other codecs have smaller memory requirements).
If one needs more for particular use case, one can use "mem" module
parameter to force larger (or smaller) buffer (for example by adding
"s5p_mfc.mem=16M" to kernel command line).

[mchehab@s-opensource.com: fix two checkpatch warnings: don't initialize
 static to NULL; don't use S_foo permisions]

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Andrzej Hajda <a.hajda@samsung.com>
Tested-by: Smitha T Murthy <smitha.t@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>