arm64: dts: qcom: msm8996: Define parent clocks for gcc

The CLKREF clocks in GCC are parented by RPM_SMD_LN_BB_CLK, through the
CXO2 pad. Wire this up so that this is properly enabled when need by the
various PHYs.

Reviewed-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20200106080546.3192125-3-bjorn.andersson@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>