arm64: dts: renesas: r8a7795: add usb-dmac ch2 and ch3 device nodes

This patch adds support for usb-dmac ch2 and ch3 device nodes for
R-Car H3 ES2.0.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>