Previously, blits using the "blorp" mechanism only worked for 8-bit
RGBA color buffers, 24-bit depth buffers, and 8 bit stencil buffers.
This was not enough, because the blorp mechanism must be used for
blitting whenever MSAA is in use.  This patch allows all formats to be
used, provided the source and destination formats match.

So far I have confirmed that the following formats work properly with
MSAA:
- GL_RGB
- GL_RGBA
- GL_ALPHA
- GL_ALPHA4
- GL_ALPHA8
- GL_R3_G3_B2
- GL_RGB4
- GL_RGB5
- GL_RGB8
- GL_RGB10
- GL_RGB12
- GL_RGB16
- GL_RGBA2
- GL_RGBA4
- GL_RGB5_A1
- GL_RGBA8
- GL_RGB10_A2
- GL_RGBA12
- GL_RGBA16

Fixes piglit tests "EXT_framebuffer_multisample/formats {2,4}" on
Sandy Bridge and Ivy Bridge.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>