net: ipa: enable IPA interrupt handlers separate from registration

Expose ipa_interrupt_enable() and have functions that register
IPA interrupt handlers enable them directly, rather than having the
registration process do that.  Do the same for disabling IPA
interrupt handlers.

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