clk: qcom: mdss: Add 8992 to 20nm pll supported devices

Add 8992 to 20nm pll supported devices.

Change-Id: Ic5ca0dc72b83da7a559cfbad1c748b25d1542919
[veeras@codeaurora.org: As part of 3.18 upgrade,
remove all non-display related code changes from the commit
	include/dt-bindings/clock/msm-clocks-8992.h]
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>