meta: Store precompiled msaa shaders for all supported sample counts

Currently, BLIT_MSAA_SHADER_2D_MULTISAMPLE_RESOLVE* and
BLIT_MSAA_SHADER_2D_MULTISAMPLE_ARRAY_RESOLVE* shaders
in setup_glsl_msaa_blit_shader() are not recompiled
when the source buffer sample count changes. For example,
implementation continued using a 4X msaa shader, even if
source buffer changes from 4X msaa to 8x msaa. It causes
incorrect rendering.

This patch adds new enums in blit_msaa_shader, one for
each supported sample count, and uses them to store
msaa shaders.

Fixes following piglit tests on Broadwell:
ext_framebuffer_multisample-accuracy all_samples color
ext_framebuffer_multisample-accuracy all_samples depth_draw
ext_framebuffer_multisample-accuracy all_samples depth_resolve
ext_framebuffer_multisample-accuracy all_samples stencil_draw
ext_framebuffer_multisample-accuracy all_samples stencil_resolve
ext_framebuffer_multisample-formats all_samples

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jason Ekstarnd <jason@jlekstrand.net>
meta: Implement ext_framebuffer_multisample_blit_scaled extension

Extension enables doing a multisample buffer resolve and buffer
scaling using a single glBlitFrameBuffer() call. Currently, we
have this extension implemented in BLORP which is only used by
SNB and IVB. This patch implements the extension in meta path
which makes it available to Broadwell.

Implementation features:
 - Supports scaled resolves of 1X, 2X, 4X and 8X multisample buffers.

 - Avoids unnecessary shader compilations by storing the pre compiled
   shaders for each supported sample count.

 - Uses bilinear filtering for both GL_SCALED_RESOLVE_FASTEST_EXT and
   GL_SCALED_RESOLVE_NICEST_EXT filter options. Although, extension
   allows this behavior, it'll be nice to use trilinear or anistropic
   filtering for GL_SCALED_RESOLVE_NICEST_EXT filter. I'll work on it
   after pushing this series.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
i965: Enable EXT_framebuffer_multisample_blit_scaled for gen8

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>