meta: Recompile msaa color resolve shader when the sample count changes

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.

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>
meta: Avoid shader recompilation for msaa color resolve blit

Currently, setup_glsl_msaa_blit_shader() doesn't store compiled
msaa shaders generated for specific sample counts. This causes
the recompilation BLIT_MSAA_SHADER_2D_MULTISAMPLE_RESOLVE* and
BLIT_MSAA_SHADER_2D_MULTISAMPLE_ARRAY_RESOLVE* shaders every
time there is a change in source buffer sample count. This can
hit the performance of an application which continuously changes
sample count of multisample buffer. Unnecessary compilations can
be avoided by storing the compiled shaders for all supported
sample counts.

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

---
This patch continues with the current approach of storing the
compiled shaders in msaa_shaders array. But, as suggested by
Ken, a better approach in the future would be to implement a
shader cache for meta and maintain a program key for each
shader. Any changes to the program key will trigger the
recompilation of the shader. It'll be similar to
brw_blorp_blit_prog_key used for blit shaders in i965 BLORP
backend. I'll keep this task in my todo list but not planning
to pick it up anytime soon. Feel free to take it off my list.
meta: Implement ext_framebuffer_multisample_blit_scaled extension
meta msaa blit scaled rendering fix
Refactoring
meta: Add 2x msaa scaled blit