ARM: dts: r8a7745: Add IIC cores to dtsi

Add iic0 and iic1 nodes to SoC dtsi. Also, define aliases i2c6
and i2c7. Board specific DT files will enable the interfaces
if needed.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>