Use gfx11-generic targets

[cgmb]

The gfx11-generic build target would reduce build times and binary size by replacing four ISAs with one.

[cgmb]

There is a bug in rocm_check_target_ids, so making the target optional would require ROCm/rocm-cmake#265.

[cgmb]

The gfx11-generic target requires -mcode-object-version=6 for amdclang++ older than ROCm 6.4. Using COV6 with versions of clang from before this December commit will result in a warning that "code object v6 is still in development and not ready for production use yet."

[cgmb]

The User Guide for AMDGPU Backend has some excellent information about the generic targets. For gfx12-generic, there should be no drawbacks. For gfx11-generic, there are some instruction restrictions that may or may not affect performance.

I'm happy to see the tests passing, but I think I will split this into two PRs because the gfx12-generic update is a no-brainer and the gfx11-generic update may require a bit of consideration.

[ammallya]

Imported to ROCm/rocm-libraries