G2D: attempt loading 'g2d_23' kernel module

It might be not statically compiled into kernel (for example in Fedora),
so we should try to explictly load it.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
G2D: enable accelerated blits for 16bpp color depth

This is still not perfect, because G2D can't saturate memory bandwidth
for this color depth (it is fillrate limited). We should emulate 16bpp blits
with 32bpp blits whenever it is possible.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>