arch: Improve the regular expression that finds operands.

This regular expression currently has a negative lookbehind assertion
that the operand name isn't preceded by any numbers or letters. Expand
that to also include the : character, since no operand should have a
namespace specifier in front of it.

Change-Id: I0bd84b69b9dad278191831d82db762ae75ce4bf1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49751
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/isa_parser/isa_parser.py

@@ -1488,7 +1488,7 @@ StaticInstPtr
         extensions = self.operandTypeMap.keys()
 
         operandsREString = r'''
-        (?<!\w)      # neg. lookbehind assertion: prevent partial matches
+        (?<!\w|:)     # neg. lookbehind assertion: prevent partial matches
         ((%s)(?:_(%s))?)   # match: operand with optional '_' then suffix
         (?!\w)       # neg. lookahead assertion: prevent partial matches
         ''' % ('|'.join(operands), '|'.join(extensions))