[AMDGPU] Don't check for VMEM hazards on GFX10

The hazard where a VMEM reads an SGPR written by a VALU counts as a data
dependency hazard, so no nops are required on GFX10. Tested with Vulkan
CTS on GFX10.1 and GFX10.3.

Differential Revision: https://reviews.llvm.org/D97926