This decouples initializing a texture layout/miptree description
from an actual texture creation, it also partially unifies texture_create
and texture_from_handle.
r300_texture inherits r300_texture_desc, which inherits u_resource.
The CBZB clear criteria are moved to r300_texture_desc::cbzb_allowed[level].
And other minor cleanups.
d779a5d16a