net: ipa: reduce IPA version assumptions

Modify conditional tests throughout the IPA code so they do not
assume that IPA v3.5.1 is the oldest version supported.  Also remove
assumptions that IPA v4.5 is the newest version of IPA supported.

Augment versions in comments with "+", to be clearer that the
comment applies to a version and subsequent versions.  (E.g.,
"present for IPA v4.2+" instead of just "present for v4.2".)

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>