arm64: zynqmp: Configure SoC RTC on SOM

arm64: zynqmp: Configure SoC RTC on SOM

Use RTC available in HW on Kria SOM without using emulation that's why
configure it properly and disable emulated one.
Power on reset value of RTC Calibration register without battery backup is
not matching with crystal frequency which leads to RTC time drift. That's
why write CALIB_WRITE register with crystal frequency (0x7FFF). There is
also an option to write zero so that Linux will set default value (0x7FFF)
in driver probe but calibration 0 is not permited by DT schema.

Co-developed-by: Srinivas Goud <srinivas.goud@amd.com>
Signed-off-by: Srinivas Goud <srinivas.goud@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/9b684faeec85381b9b8fe796aaebc2ee79f17b8e.1729663761.git.michal.simek@amd.com