readclock: add support for am335x RTC

Add support for getting/setting the am335x SoC's internal real
time clock. Also, allow the power off alarm to be set.

Make readclock an "always on" driver. This is needed for setting
power-off alarms whenever the power button is pressed on the BBB.

Replace the readclock.sh script & single run driver with a
readclock program that takes the same arguments and forwards
the requests on to the always up readclock driver.

Change-Id: Ifd6c2acd80ae4b5e79d83df510df445c24e24a71

etc/rc

@@ -124,17 +124,9 @@ start)
     then . "$RC_TZ"
     fi
 
-    if [ $ARCH = i386 ]
-    then
-	# Try to read the hardware real-time clock, otherwise do it manually.
-	readclock || intr date -q
-    fi
-
-    if [ $ARCH = earm ]
-    then
-	date 201301010000
-    fi
-  
+    # Start real time clock driver & set system time, otherwise default date.
+    up readclock.drv
+    readclock || date 201301010000
 
     # Initialize files.
     >/etc/utmp				# /etc/utmp keeps track of logins

etc/system.conf

@@ -299,9 +299,12 @@ service random
 
 service readclock.drv
 {
+	ipc	ALL;
 	io	70:2;
 	system
+		PRIVCTL		# 4
 		UMAP		# 14
+		VIRCOPY		# 15
 		DEVIO		# 21
 		READBIOS	# 35
 	;