net: ipa: register IPA interrupt handlers directly

Declare the microcontroller IPA interrupt handler publicly, and
assign it directly in ipa_interrupt_config().  Make the SUSPEND IPA
interrupt handler public, and rename it ipa_power_suspend_handler().
Assign it directly in ipa_interrupt_config() as well.

This makes it unnecessary to do this in ipa_interrupt_add().  Make
similar changes for removing IPA interrupt handlers.

The next two patches will finish the cleanup, removing the
add/remove functions and the handler array entirely.

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