ARM: dts: msm: Add 600Mhz GPU clock support for SDM450

SDM450 GPU can support max 600Mhz clock. Add support
for new GPU powerlevel.

Change-Id: If2eabd74065e3b2417b840d79c982f7495646a02
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>