intel: Add multisample scaled blitting in blorp engine

intel: Add multisample scaled blitting in blorp engine

In traditional multisampled framebuffer rendering, color samples must be
explicitly resolved via BlitFramebuffer before doing the scaled blitting
of the framebuffer. So, scaled blitting of a multisample framebuffer
takes two separate calls to BlitFramebuffer.

This patch implements the functionality of doing multisampled scaled
resolve using just one BlitFramebuffer call. Important changes involved
in this patch are listed below:
    - Use float registers to scale and offset texture coordinates.
    - Change offset computation to consider float coordinates.
    - Round the scaled coordinates down to nearest integer.
    - Modify src texture coordinates clipping to account for scaling..
    - Linear filter is not yet implemented in blorp. So, don't use
      blorp engine to do single sampled scaled blitting.

V3: Fix nearest filtering issue in scaled blits. Makes failing piglit
fbo-blit-stetch test and framebuffer_blit_functionality_magnifying_blit.test
in gles3 CTS pass.

Observed no piglit, gles3 CTS regressions on sandybridge & ivybridge with
this patch.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>