dt-bindings: rtc: qcom-pm8xxx-rtc: Add qcom pm8xxx rtc bindings

Add binding doc for qcom pm8xxx rtc device.

Signed-off-by: satya priya <skakit@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1617976766-7852-5-git-send-email-skakit@codeaurora.org