intel_batchbuffer: add support for non-32bit blt copies

Needed by an upcoming patch fixing kms_render's blits for fbs that have
other than 32bpp formats.

Based on the corresponding SNA function.

Signed-off-by: Imre Deak <imre.deak@intel.com>
lib: export drm_format_to_bpp

Needed by the next patch.

Signed-off-by: Imre Deak <imre.deak@intel.com>
kms_render: fix gpu-blit for non-32bit bpps

intel_copy_bo assumes a 32bpp bo, whereas we passed it bos with
arbitrary bpp values. This resulted in trashing GPU memory following the
destination bo.

Fix this by using a blit helper that can handle other bpps too.

Signed-off-by: Imre Deak <imre.deak@intel.com>