msm: clock: Introduce device tree lookups

Add a function of_msm_clock_register that registers a
clock provider with the clock DT framework. Provide a
new CLK_LOOKUP_OF macro to link up clock lookup entries
with DT clock indices.

Change-Id: I66ab29df116341583db5f812b2dc5db3a65e15b5
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>