arm64: zynqmp: dts: Add rts delay property for rs485 mode on KD240

Add "rs485-rts-delay" property to uartps node with delay_rts_before_send
and delay_rts_after_send values as 10ms for rs485 mode on KD240.

10ms rts delay values have been chosen based on testing with rs485
temperature sensor (which is part of the kit) as safe minimum value
for reliable operation at a baud rate of 9600.

Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/0e0c4c067236e11f661c1d067017e1ca975c9ddb.1721297721.git.michal.simek@amd.com