ARM: S3C64XX: Save/restore S3C64XX_SDMA_SEL on suspend/resume

This patch makes sure that S3C64XX_SDMA_SEL register is preserved during
sleep mode, as it is critical for DMA operation and the DMA driver alone
does not provide any power management facilities.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>