rtc: zynqmp: use dynamic max and min offset ranges

rtc: zynqmp: use dynamic max and min offset ranges

Maximum and minimum offsets in ppb that can be handled are dependent on
the rtc clock frequency and what can fit in the 16-bit register field.

Reviewed-by: Harini T <harini.t@amd.com>
Tested-by: Harini T <harini.t@amd.com>
Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Link: https://patch.msgid.link/20260122-zynqmp-rtc-updates-v4-5-d4edb966b499@vaisala.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>