regulator: Fix build breakage on !REGULATOR

regulator: Fix build breakage on !REGULATOR

Add missing stubs for regulator_suspend_prepare() and
regulator_suspend_finish() to fix exynos_defconfig build without
REGULATOR:

arch/arm/mach-exynos/built-in.o: In function `exynos_suspend_finish':
arch/arm/mach-exynos/suspend.c:537: undefined reference to `regulator_suspend_finish'
arch/arm/mach-exynos/built-in.o: In function `exynos_suspend_prepare':
arch/arm/mach-exynos/suspend.c:520: undefined reference to `regulator_suspend_prepare'
make: *** [vmlinux] Error 1

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reported-by: Joerg Roedel <joro@8bytes.org>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>