R600/SI: Add intrinsics for texture sampling with user derivatives

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600/SI: Initial support for LDS/GDS instructions

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600/SI: Add intrinsic for retrieving the current thread ID

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600/SI: Add pattern for the AMDGPU.barrier.local intrinsic

lit test coverage to follow in the next commit.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
R600/SI: Initial local memory support

Enough for the radeonsi driver to use it for calculating derivatives.

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>