[AMDGPU] Update dlc usage for GFX11

In GFX10 dlc controlled L1 cache bypass. In GFX11 it has been repurposed
to control MALL NOALLOC, and glc controls L1 as well as L0 cache bypass.

Update the documentation and SIMemoryLegalizer accordingly. Set dlc for
nontemporal and volatile accesses.

Differential Revision: https://reviews.llvm.org/D127405