msm: clock-9625: Add ipa sleep clk support

gcc_ipa_sleep_clk is a clock that the IPA core needs to use. Add the
support of this clock in the clock driver.

Change-Id: I7c15a86d84d5af934a60f8a9e2bb85e04b32d0af
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>