am33xx: Make SoC bootcount driver have its own symbol

Some am33xx boards may not use the RTC block for bootcount (as it may
not be wired up for the board) and use some other facility.  So add
another symbol for the bootcount driver for the IP block.

Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Tom Rini <trini@ti.com>

drivers/bootcount/bootcount_davinci.c

@@ -2,6 +2,10 @@
  * (C) Copyright 2011
  * Heiko Schocher, DENX Software Engineering, hs@denx.de.
  *
+ * A bootcount driver for the RTC IP block found on many TI platforms.
+ * This requires the RTC clocks, etc, to be enabled prior to use and
+ * not all boards with this IP block on it will have the RTC in use.
+ *
  * SPDX-License-Identifier:	GPL-2.0+
  */