freedreno/a6xx: add support for dual-source blending
It was already implemented in Turnip !5039 (merged).
Also, while implementing this I found that in freedreno
SP_FS_OUTPUT_CNTL0 is emitted with
0xfc000000 constant. It is
A6XX_SP_FS_OUTPUT_CNTL0_STENCILREF_REGID which is already used in Turnip. So, I guess I'll implement
On irc it was discussed that dual src blending is the only thing which prevents GL3.3 support, I ran CTS for GL3.3 and there are a few failures, I'll check them.