i965/blorp: Rework hiz rect alignment calculations

i965/blorp: Rework hiz rect alignment calculations

At the moment, the minify operation does nothing because
params.depth.view.base_level is always zero.  However, as soon as we start
using actual base miplevels and array slices, we are going to need the
minification.  Also, we only need to align the surface dimensions in the
case where we are operating on miplevel 0.  Previously, it didn't matter
because it aligned on miplevel 0 and, for all other miplevels, the miptree
code guaranteed that the level was already aligned.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>