ARM: dts: am335x-boneblack: enable power off and rtc wake up

Configure the RTC as system-power controller, which allows the system to
be powered off as well as woken up again on subsequent RTC alarms.

Note that the PMIC needs to be put in SLEEP (rather than OFF) mode to
maintain RTC power.  Specifically, this means that the PMIC
ti,pmic-shutdown-controller property must be left unset in order to be
able to wake up on RTC alarms.

Tested on BeagleBone Black (rev A5).
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Tested-by: Felipe Balbi <balbi@ti.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Benot Cousson <bcousson@baylibre.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: Keerthy J <j-keerthy@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/boot/dts/am335x-boneblack.dts

@@ -80,3 +80,7 @@ hdmi {
 		status = "okay";
 	};
 };
+
+&rtc {
+	ti,system-power-controller;
+};