msm: clock: Add a flag to disable rate caching

Certain clocks can have the rate of their parent
changed without clk_set_rate being called on them.
Caching rates for these clocks is incorrect, since
their rates may have changed since the last
clk_set_rate.

Change-Id: I1eb5dded6093f5ccd2b43a4d89eca033db54b73f
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>