net: ipa: move IPA power operations to ipa_clock.c

Move ipa_suspend() and ipa_resume(), as well as the definition of
the ipa_pm_ops structure into "ipa_clock.c".  Make ipa_pm_ops public
and declare it as extern in "ipa_clock.h".

This is part of centralizing IPA power management functionality into
"ipa_clock.c" (the file will eventually get a name change).

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