xtensa: Tweak xuartps UART driver Rx watermark for Cadence CSP config.

Add module parameter xilinx_uartps.rx_trigger_level=32 to command line
options for CSP to set Rx watermark for xuartps driver lower than the
default value, to avoid UART overruns at 115200 bps.
Signed-off-by: NScott Telford <stelford@cadence.com>
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

arch/xtensa/boot/dts/csp.dts

@@ -7,7 +7,7 @@
 	interrupt-parent = <&pic>;
 
 	chosen {
-		bootargs = "earlycon=cdns,0xfd000000,115200 console=tty0 console=ttyPS0,115200 root=/dev/ram0 rw earlyprintk loglevel=8 nohz=off ignore_loglevel";
+		bootargs = "earlycon=cdns,0xfd000000,115200 console=tty0 console=ttyPS0,115200 root=/dev/ram0 rw earlyprintk xilinx_uartps.rx_trigger_level=32 loglevel=8 nohz=off ignore_loglevel";
 	};
 
 	memory@0 {