msm: camera: Improve interface for large SPI reads

For each SPI read, two buffers of read size + header need to be
allocated.  These allocation might fail if read size is large.  It's also
expensive to allocate memory each time for repeated transfers.
Therefore, msm_camera_spi_read_seq_l() is provided to use pre-allocated
buffers instead of allocating them each time.

Change-Id: Ibd52fd26bb0a4fdd913bef9c2bfc410152245c3b
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>