arm64: dts: qcom: sa8540p-ride: enable rtc

arm64: dts: qcom: sa8540p-ride: enable rtc

SA8540P-ride is one of the Qualcomm platforms that does not have access
to UEFI runtime services and on which the RTC registers are read-only,
as described in:
https://lore.kernel.org/all/20230202155448.6715-1-johan+linaro@kernel.org/

Reserve four bytes in one of the PMIC registers to hold the RTC offset
the same way as it was done for sc8280xp-crd which has similar
limitations:
    commit e67b45582c5e ("arm64: dts: qcom: sc8280xp-crd: enable rtc")

On SA8540P-ride, the register bank SDAM6 of the first PMIC is not
writable. Following recommendations provided during the review, use
SDAM2 from the second PMIC at offset 0xa0 instead.

Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Signed-off-by: Eric Chanudet <echanude@redhat.com>
Link: https://lore.kernel.org/r/20230809203506.1833205-1-echanude@redhat.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>