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/score/Kconfig

@@ -11,7 +11,6 @@ config SCORE
        select ARCH_DISCARD_MEMBLOCK
        select GENERIC_CPU_DEVICES
        select GENERIC_CLOCKEVENTS
-       select GENERIC_IDLE_LOOP
        select HAVE_MOD_ARCH_SPECIFIC
 	select VIRT_TO_BUS
 	select MODULES_USE_ELF_REL