msm: clock: Expose parts of "clock.h" through <mach/clk-provider.h>

Expose the features of "clock.h" outside of mach-msm so that new clock
drivers leveraging the framework in mach-msm/clock.c can be implemented
outside of the mach-msm sub-architecture directory.

Change-Id: I3d07017388b28d4e5b6e930e7eda4f48e840714b
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>