arm64: dts: qcom: msm8916: Add fixed rate on-board oscillators

Currently the rates of the xo and sleep clocks are hard-coded in the
GCC driver, but this is a board layout description that actually should
be in the DT. Moving them into DT also allows us to insert the RPM
controlled clocks between the DT and GCC clocks.

Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>