LLVM is going to support the legacy instructions soon.

This change switches FMA to MAD for gfx10.

54793 shaders in 33659 tests
Totals:
SGPRS: 2632554 -> 2629570 (-0.11 %)
VGPRS: 1536364 -> 1535312 (-0.07 %)
Spilled SGPRs: 3602 -> 3562 (-1.11 %)
Spilled VGPRs: 44 -> 40 (-9.09 %)
Private memory VGPRs: 256 -> 256 (0.00 %)
Scratch size: 312 -> 308 (-1.28 %) dwords per thread
Code Size: 55422660 -> 55345408 (-0.14 %) bytes
Max Waves: 963983 -> 964200 (0.02 %)

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <!6756>