spi/s3c64xx: Ensure runtime PM is enabled prior to registration

Otherwise we may try to start transfers immediately and then fail to
runtime resume the device causing us not to have clocks enabled.

Signed-off-by: Mark Brown <broonie@linaro.org>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>

Conflicts:
	drivers/spi/spi-s3c64xx.c