[llvm] [AMDGPU][GlobalIsel] Use isRegisterClassType to check for legal types for G_FREEZE & G_IMPLICIT_DEF (PR #101331)

[via llvm-commits]

================
@@ -186,23 +184,6 @@ body: |
     %1:_(s32) = G_LOAD %0 :: (load (s32) from %ir.tmp1)
 ...
 
----
-name: non_power_of_2
----------------
sstipanovic wrote:

Because this test assumes that the input is already legalized, but S448 is not legal.

https://github.com/llvm/llvm-project/pull/101331