clk: qcom: Add support for msm8994 global clock controller

The clock definition was ported from the Google 3.10 kernel tree to
work with the latest kernel.

Signed-off-by: Bastian Köcher <mail@kchr.de>
[jeremymc@redhat.com: created new commit of just dt-bindings]
Signed-off-by: Jeremy McNicoll <jeremymc@redhat.com>
[sboyd@codeaurora.org: Tidy up commit text and Kconfig help]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>