[clang] AMDGPU: Remove "gws" from the “read-only” target feature list (PR #148141)

[Changpeng Fang via cfe-commits]

changpeng wrote:

Thanks @yxsamliu and @arsenm for the suggestions. Now we mark these features as read-only if and only if the target supports them. The "ReadOnly" logic still works as it is supposed to.

https://github.com/llvm/llvm-project/pull/148141