[AMDGPU] Add maximum NSA size limit ISA feature

Add maximum NSA size limit as an ISA feature.
Use this to reduce NSA usage on GFX10.1 to avoid stability issues
with 4 and 5 dwords NSA instructions.
Maintain use of longer NSA instructions on GFX10.3.

Note: this also contains some minor fixes for GlobalISel which
did not work correctly with non-NSA form instructions on GFX10.

Reviewed By: foad

Differential Revision: https://reviews.llvm.org/D103348