[llvm] [RISCV] Correct the immediate swizzling for P-ext plui.h/w. (PR #149945)

[Sam Elliott via llvm-commits]

================
@@ -148,11 +162,11 @@ def PSSLAI_W : RVPUnaryImm5<0b101, "psslai.w">;
 } // Predicates = [HasStdExtP, IsRV64]
 
 let Predicates = [HasStdExtP] in
-def PLI_H : RVPLoadImm10<0b1011000, "pli.h">;
+def PLI_H : PLI_i<0b1011000, "pli.h">;
 let Predicates = [HasStdExtP, IsRV64] in
-def PLI_W : RVPLoadImm10<0b1011001, "pli.w">;
+def PLI_W : PLI_i<0b1011001, "pli.w">;
 let Predicates = [HasStdExtP] in
-def PLI_B : RVPLoadImm8<0b10110100, "pli.b">;
+def PLI_B : PLI_B_i<0b10110100, "pli.b">;
----------------
lenary wrote:

This is not quite the bug you're trying to fix, so it can be done separately, but `PLI.B` in the spec expects `imm[9:8] == 0`, and we're not really enforcing that.

https://github.com/llvm/llvm-project/pull/149945