mmc: S5P: Support DMA restarts at buffer boundaries

Currently if a DMA buffer straddles a buffer alignment boundary
(512KiB) then the DMA engine will pause and generate a DMA
interrupt.  Since the DMA interrupt is not enabled it will hang
the MMC driver.

This patch adds support for restarting the DMA transfer.  The
SYSTEM_ADDRESS register contains the next address that would have
been read/written when a boundary is hit.  So we can read that
and write it back.  The write triggers the resumption of the
transfer.

Signed-off-by: Anton Staaf <robotboy@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Tested-by : Jaehoon Chung <jh80.chung@samsung.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>