ARM: OMAP2+: hwmod: RTC: Add lock and unlock functions

RTC IP have kicker feature which prevents spurious writes to its registers.
In order to write into any of the RTC registers, KICK values has to be
written to KICK registers. Also, RTC busy flag needs to be polled for
non-TC registers as well, without which update is not proper and confirmed
it by testing on DRA7-evm.
Introduce omap_hwmod_rtc_unlock/lock functions, which  writes into these
KICK registers inorder to lock and unlock RTC registers.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[paul@pwsan.com: fixed subject line]
Signed-off-by: Paul Walmsley <paul@pwsan.com>
diff --git a/arch/arm/mach-omap2/omap_hwmod.h b/arch/arm/mach-omap2/omap_hwmod.h
index 7c7a311..4041bad 100644
--- a/arch/arm/mach-omap2/omap_hwmod.h
+++ b/arch/arm/mach-omap2/omap_hwmod.h
@@ -754,6 +754,8 @@
  */
 
 extern int omap_hwmod_aess_preprogram(struct omap_hwmod *oh);
+void omap_hwmod_rtc_unlock(struct omap_hwmod *oh);
+void omap_hwmod_rtc_lock(struct omap_hwmod *oh);
 
 /*
  * Chip variant-specific hwmod init routines - XXX should be converted