ARM: shmobile: r8a73a4 dtsi: Add SoC-specific IIC compatible properties

The IIC nodes used the generic compatible properties only.
This may cause the driver to fail when using Standard Speed on IIC
masters where the operational clock is driven by the 130 MHz HP clock.

Add the SoC-specific compatible property to fix this.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>