mesa: Add error checking in _mesa_BlitFramebuffer() for MRTs

mesa: Add error checking in _mesa_BlitFramebuffer() for MRTs

This patch adds required error checking in _mesa_BlitFramebuffer() when
blitting to multiple color render targets. It also fixes a case when
blitting to a framebuffer with renderbuffer/texture attached to
GL_COLOR_ATTACHMENT{i} (where i!=0). Earlier it skips color blitting if
nothing is found attached to GL_COLOR_ATTACHMENT0.

V2: Fixed a case when number of draw buffer attachments are zero.
V3: Do compatible_color_datatypes() and compatible_resolve_formats()
    check for all the draw renderbuffers in fbobject.c. Fix debug code
    at bottom of _mesa_BlitFramebuffer() to handle MRTs. Combine error
    checking code for linear blits with other color blit error checking.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>