msm: ipa: add support for IPA clock gating

IPA driver adds a request for the gcc_ipa_clk only. Other clocks are
managed internally by clock driver and bus driver.
IPA driver requests nominal clock rate (150 MHz) for the gcc_ipa_clk.

Change-Id: I397174f706468e159815557ad9f706b61bb871b0
Signed-off-by: Ravit Katzav <rkatzav@codeaurora.org>