s5p-fimc: Iterate for each memory plane

Depth and payload is defined per memory plane. It's better to iterate using
number of memory planes. this was not causing much issue since the rest
of the arrays involved where intialized to zero.
s5p-fimc: Fix YUV422P depth

All YUV 422 has 16bit per pixels.
s5p-fimc: Reuse calculated sizes

This formula did not take into account the required tiled alignement for
NV12MT format. As this was already computed an store in payload array
initially, simply reuse that value.
s5p-fimc: Don't allow application to choose the buffer size

This is not allowed by the spec, and only served the purpose of hiding bugs
in size calculation so far.