llvmpipe: integrate memory allocation into llvmpipe_texture_layout

llvmpipe: integrate memory allocation into llvmpipe_texture_layout

Seems pointless to just duplicate some of the calculations (the calculation
of actual memory used compared to what was predicted in llvmpipe_texture_layout
actually could have differed slightly in some cases due to different alignment
rules used though this should have been of no consequence).

v2: keep the previous mip alignment of MAX2(64, cacheline). This was added for
ARB_map_buffer_alignment - I'm not convinced it's needed for textures, but
it was supposed to be cleanup without functional change. Also replace div
with 64bit mul / comparison.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>