dm: timer: uclass: add timer init in uclass driver to add timer device

Adding timer init function in timer-uclass driver to create and
initialize the timer device on platforms where u-boot,dm-pre-reloc
is not used. Since there will be multiple timer devices in the
system, adding a tick-timer node in chosen node to know which
timer device to be used as tick timer in u-boot.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>

include/timer.h

@@ -7,6 +7,15 @@
 #ifndef _TIMER_H_
 #define _TIMER_H_
 
+/*
+ * dm_timer_init - initialize a timer for time keeping. On success
+ * initializes gd->timer so that lib/timer can use it for future
+ * referrence.
+ *
+ * @return - 0 on success or error number
+ */
+int dm_timer_init(void);
+
 /*
  * timer_conv_64 - convert 32-bit counter value to 64-bit
  *