i965/blorp: store x and y offsets in brw_blorp_mip_info.

i965/blorp: store x and y offsets in brw_blorp_mip_info.

Currently, gen{6,7}_blorp_emit_surface_state assumes that the src and
dst surfaces are mapped to miplevel 0 and layer 0 (thus no surface
offset is required).  This is a bug, since the user might try to blit
to and from levels/layers other than 0.

To fix this bug, it will not be sufficient to have
gen6_{6,7}_blorp_emit_surface_state look up the surface offset at the
time they set up the surface state, since these offsets will need to
be tweaked when blitting stencil buffers (due to the fact that stencil
buffer blits have to swizzle between W and Y tiling formats).

So, to pave the way for the bug fix, this patch causes the x and y
offsets to be computed during blit setup and stored in
brw_blorp_mip_info.

As a result of this change, brw_blorp_mip_info doesn't need to store
the level and layer anymore.

For consistency, this patch makes a similar change to the handling of
depth buffers when doing HiZ operations.

NOTE: This is a candidate for stable release branches.

Reviewed-by: Eric Anholt <eric@anholt.net>