RTC: Disable CONFIG_RTC_CLASS from being built as a module

The RTC subsystem has a number of accessors that are available via
include/linux/rtc.h. However many of these interfaces are not
available for use if CONFIG_RTC_CLASS=m.

So in order to support wider use of the RTC in the kernel, I'm
removing the tristate config option for a bool, so that code can
easily be conditionalized if the RTC class is present or not.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/rtc/Kconfig

@@ -3,10 +3,10 @@
 #
 
 config RTC_LIB
-	tristate
+	bool
 
 menuconfig RTC_CLASS
-	tristate "Real Time Clock"
+	bool "Real Time Clock"
 	default n
 	depends on !S390
 	select RTC_LIB
@@ -15,9 +15,6 @@ menuconfig RTC_CLASS
  	  be allowed to plug one or more RTCs to your system. You will
 	  probably want to enable one or more of the interfaces below.
 
-	  This driver can also be built as a module. If so, the module
-	  will be called rtc-core.
-
 if RTC_CLASS
 
 config RTC_HCTOSYS