[media] davinci: vpif capture: size up the memory for the buffers from the buffer pool

Size up the memory for the buffers from the buffer pool allocated in board
file.  Then adjust the reqbuf count depending the available memory.

Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>