ARM: shmobile: r8a7740: add DMAEngine support for FSI

Current shdmac can support FSI DMAC on r8a7740.
This support reduce CPU duty when sound was playback.

This patch is based on v1.0 manual

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>