net: ipa: update IPA version comments in "ipa_reg.h"

Some definitions in "ipa_reg.h" are only valid for certain versions
of IPA.  In such cases a comment indicates a version or range of
versions where the definition is (or is not) valid.  Almost all such
cases look like "IPA vX.Y", but a few don't include the "IPA" tag.

Update these so they all consistently include "IPA".  And replace
a few lines that talk about "the next bit" in the definition of the
ipa_irq_id enumerated type with a more concise comment using the
"IPA vX.Y" convention.

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