tests, base: Removed ambiguity from base/intmath.hh

tests, base: Removed ambiguity from base/intmath.hh

The function intmath.leastSigBit is ambiguous given
its name. It does not return the value of the least
significant bit, or the position of the least significant
set bit, but instead 2 to the power of the position of
the least significant set bit. It has thereby been removed
and the function intmath.isPowerOf2 has been refactored to
not require intmath.leastSigBit.

Change-Id: I22479c666cdd059865b8c73b70b5388f98a4584d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22583
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>