msm: clock-generic: Move the clock-generic header to include/linux/clk

Architectural changes in the ARM Linux kernel tree mandate
the eventual removal of the mach-* directories. Move the
clock-generic header to support this.

Change-Id: I6876f60f7d23dfe162a2b13a374eb4c4b2856df4
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>