i965: Support multisampling in surface_state for textures

i965: Support multisampling in surface_state for textures

The surface_state setup for renderbuffers already worked; only the
texturing side needed work. BLORP does something similar, but does its
own surface_state setup.

On Gen6, we just need to set the correct sample count.

On Gen7: - set the correct sample count
         - set the correct layout mode
         - set GEN7_SURFACE_ARYSPC_LOD0 if it's set in the miptree.

V2: - Clarify commit message
    - Rebased onto Paul's physical/logical dims cleanup
    - Added Gen7 support

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Paul Berry <stereotype441@gmail.com>