arch: Improve the regular expression that finds operands.
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 <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Reviewed-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5