idle: Remove GENERIC_IDLE_LOOP config switch

All archs are converted over. Remove the config switch and the
fallback code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/c6x/Kconfig

@@ -18,7 +18,6 @@ config C6X
 	select OF_EARLY_FLATTREE
 	select GENERIC_CLOCKEVENTS
 	select MODULES_USE_ELF_RELA
-	select GENERIC_IDLE_LOOP
 
 config MMU
 	def_bool n