drm/radeon/kms: r600 CS parser fixes

- buffer offsets in the base regs are 256b aligned so
shift properly when comparing, fixed by Andre Maasikas
- mipmap size was calculated wrong when nlevel=0
- texture bo offsets were used after the bo base address was added
- vertex resource size register is size - 1, not size

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: Andre Maasikas <amaasikas@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>