arm64: dts: renesas: r8a7795: Add missing SYS-DMAC2 dmas

On R-Car H3, on-chip peripheral modules that can make use of DMA are
wired to either SYS-DMAC0 only, or to both SYS-DMAC1 and SYS-DMAC2.

Add the missing DMA properties pointing to SYS-DMAC2 for HSCIF[0-2],
SCIF[0125], and I2C[0-2].  These were initially left out because early
firmware versions prohibited using SYS-DMAC2.  This restriction has been
lifted in IPL and Secure Monitor Rev1.0.6 (released on Feb 25, 2016).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>