net: ipa: move ipa_suspend_handler()

Move ipa_suspend_handler() into "ipa_clock.c" from "ipa_main.c", to
group with the reset of the suspend/resume code.  This IPA interrupt
is triggered if an IPA RX endpoint is suspended but has a packet to
be delivered.

Introduce ipa_power_setup() and ipa_power_teardown() to add and
remove the handler for the IPA SUSPEND interrupt at the same place
as before, while allowing the handler to remain private.

The "power" naming convention will be adopted elsewhere in this
file as well (soon).

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