[AMDGPU][PATCH 2/3] Stubs implementation of the new intrinsics on Evergreen

This patch adds some stubs to provide a first implementation of the
intrinsics for barriers and memory fences on EG. The barrier.nofence()
intrinsic is the only intrinsic correctly implemented (for sure)
with this patch. Maybe the barrier.local() intrinsic can be
considered ok like this as the LDS memory is atomic. The other
intrinsics need to use WAIT_ACK in some way and that we modify
the surrounding memory operations with ACK.

Signed-off-by: Damien Hilloulin <damien.hilloulin@supelec.fr>