asix-sigma: use more helpers for bit mask creation

asix-sigma: use more helpers for bit mask creation

Rename macros to better reflect which of them check a bit position, and
which span a bit field of given width. Adjust more call sites to use the
macros. This takes tedium out of maintenance as well as review. Has the
minor benefit of somewhat shortening text lines, and eliminating nested
parentheses (or getting perceived as if it would).