radeon: fix surface API for good before anyone start relying on it

The mipmap level computation was wrong, we need to know the block
width, height, depth of compressed texture to properly compute this.
Change API to provide block width, height, depth instead of nblk_x,
nblk_y, nblk_z.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>