drm/gma500: Add blitter submit ioctl

We can now validate, relocate and submit blitter commands. The buffer
relocation is very simple, we just add two 32 bit values on the position
for each buffer offset. First 32 bits are the gem handle and the second
32 bits are the offset into that buffer.

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>