clk: qcom: gcc-msm8998: Add clkref clocks

Add clkref clocks for usb3, hdmi, ufs, pcie, and usb2. They are all
sourced off CXO_IN, so parent them off "xo" until a proper link to the
rpmcc can be described in DT.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>