ARM: shmobile: r8a7740: add DMAEngine support for USB

Current shdmac can support USB DMAC on r8a7740.
This support reduce CPU duty when USB access.

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>