dts: msm8974pro: initial Krait 8974AB overclocking

Squash of commits from faux123:
dts: msm8974pro: initial Krait 8974AB overclocking
dts: adjust the regulator settings to support OC
dts: msm8974pro: overclocking tweak for 3.0 GHz
dts: regulator update for 3.0 GHz overclocking
dts: reduce OC to 2.88 GHz max

Change-Id: I07aec75884e6c4500ac19c5e298616091585b068
Signed-off-by: Paul Reioux <reioux@gmail.com>
dts: introduce 268MHz clock