[AMDGPU] Incorrect error message regarding SCC modifier (#65660)

For the AMD GFX90A GPU, the SCC instruction modifier is allowed for
certain classes of instructions. However, the current assembler
generates an error message, "scc is not supported on this GPU",
regardless of the instruciton. This fix modifies the message as well as
the logic for generating the message. Related tests are moved from
gfx90a_err.s to gfx90a_asm_features.s.

Co-authored-by: Jun Wang <jun.wang7@amd.com>