arch-x86: Fix immediate based IN instructions.

These were loading the immediate into a temporary microcode register
which would then be used to calculate the address to actually send to
the memory system. Unfortunately this was using a data size equal to the
address size, which would mean that the immediate would be merged into
that temporary, leaving previously set bits intact. The data size
*should* have been set to 8, and was already in other similar
instructions. That forces the limm microop to overwrite the temporary
entirely.

Change-Id: I87c82b4677db768ccb6401a3dbda61317c014152
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55286
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

src/arch/x86/isa/insts/general_purpose/input_output/general_io.py

@@ -39,7 +39,7 @@
 microcode = '''
     def macroop IN_R_I {
         .adjust_imm trimImm(8)
-        limm t1, imm, dataSize=asz
+        limm t1, imm, dataSize=8
         mfence
         ld reg, intseg, [1, t1, t0], "IntAddrPrefixIO << 3", addressSize=8, \
             nonSpec=True