sh: Wire up ARCH_HAS_DEFAULT_IDLE for cpuidle.

cpuidle wants ARCH_HAS_DEFAULT_IDLE defined in order to use the
default idle loop. So, make it accessible and enable it for all
sh machines.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

diff --cc arch/sh/Kconfig
Simple merge

diff --cc arch/sh/include/asm/system.h
Simple merge

diff --cc arch/sh/kernel/idle.c
Simple merge