ARM: S3C24XX: use SAMSUNG_WAKEMASK for s3c2416

Both s3c2412 and s3c2416 use the s3c2412_pm_prepare code, which
depends on the common wakemask code, but only s3c2412 currently
selects the code, leading to a build error for an s3c2416-only
kernel.

arch/arm/mach-s3c24xx/built-in.o: In function `s3c2412_pm_prepare':
:(.text+0x240): undefined reference to `samsung_sync_wakemask'
arch/arm/mach-s3c24xx/built-in.o:(.data+0xeb0): undefined reference to `s3c2412_subsys'

This adds the missing select.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene@kernel.org>