ARM: s3c64xx: select power domains only when used

The power domain code is only available when CONFIG_PM
is enabled, so we must not select that unconditionally for
s3c64xx. Changing it to 'select PM_GENERIC_DOMAINS if PM'
mirrors what we do on other platforms, and fixes a possible
randconfig build bug.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>