rtc kconfig: point out need for static linkage

Various people have expressed surprise that their modular RTC drivers don't
seem to work for initializing the system time at boot.  To help avoid such
unpleasantness, make the Kconfig text point out that the driver probably
needs to be statically linked.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: NAlessandro Zummo <a.zummo@towertech.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/Kconfig

@@ -38,6 +38,9 @@ config RTC_HCTOSYS_DEVICE
 	  clock, usually rtc0.  Initialization is done when the system
 	  starts up, and when it resumes from a low power state.
 
+	  The driver for this RTC device must be loaded before late_initcall
+	  functions run, so it must usually be statically linked.
+
 	  This clock should be battery-backed, so that it reads the correct
 	  time when the system boots from a power-off state.  Otherwise, your
 	  system will need an external clock source (like an NTP server).