ARM: SAMSUNG: Move DMA clock enable into S3C PL330 driver

This patch moves DMA clock enable functionality into pl330_probe() of
plat-samsung/s3c_pl330.c (PL330 DMAC driver) and disable functionality
into pl330_remove().
For now according to clock policy of Samsung SoCs' mainline, clocks which
are used in the driver should be controlled by each own.

Signed-off-by: Seungwhan Youn <sw.youn@samsung.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
[kgene.kim@samsung.com: minor title and comment edit]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>