util: Remove the subfunc arg from M5OP_FOREACH.

util: Remove the subfunc arg from M5OP_FOREACH.

Now that the annotation pseudo ops are removed, the subfunction is
always zero. It is no longer decoded within gem5 either. The format of
the pseudo op func/subfunc mechanism is unchanged for compatibility, but
the subfunc field will always be zero now.

Change-Id: I2167571577b6557d06aa26d8aecaca78797f5f59
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27205
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>