radeonsi: Handle TGSI_SEMANTIC_BCOLOR.

Put the back face colour right after the front face colour in the LDS parameter
space.

Fixes 18 piglit tests related to two sided lighting.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
5 files changed