net: ipa: tidy up register enum definitions

Update a few enumerated type definitions in "ipa_reg.h" so that the
values assigned to each member align on the same column.  Where a
"TX" or "RX" (or both) comment is present, move that annotation into
a separate comment between the member name and its value.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>