oshmem

The VPE was restricting the number of plane per buffer based on
the fact that if a particular format had color separation it was
meant to need 2 planes.

However NV12/NV16 are color separate format which are meant to be
presented in a single contiguous buffer/plane.
It could also be presented in a multi-plane as well if need be.
So we must support both modes for more flexibility.

The number of plane requested by user space was previously ignored
and was therefore always overwritten.
The driver now use the requested num plane as hint to calculate needed
offset when required.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>