clocksource/drivers/oxnas: Add OX820 compatible

In order to support the Oxford Semiconductor OX820 SoC, add new
compatible string to rps timer driver.
Also add new string in the dt-bindings.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/oxsemi,rps-timer.txt

@@ -2,7 +2,7 @@ Oxford Semiconductor OXNAS SoCs Family RPS Timer
 ================================================
 
 Required properties:
-- compatible: Should be "oxsemi,ox810se-rps-timer"
+- compatible: Should be "oxsemi,ox810se-rps-timer" or "oxsemi,ox820-rps-timer"
 - reg : Specifies base physical address and size of the registers.
 - interrupts : The interrupts of the two timers
 - clocks : The phandle of the timer clock source

drivers/clocksource/timer-oxnas-rps.c

@@ -295,3 +295,5 @@ err_alloc:
 
 CLOCKSOURCE_OF_DECLARE(ox810se_rps,
 		       "oxsemi,ox810se-rps-timer", oxnas_rps_timer_init);
+CLOCKSOURCE_OF_DECLARE(ox820_rps,
+		       "oxsemi,ox820se-rps-timer", oxnas_rps_timer_init);