ARM: shmobile: porter: add I2C2 DT support

Define the Porter board dependent part of the I2C2 device node.

This patch is  analogous to the commit 29a647c3 ("ARM: shmobile:
henninger: add I2C2 DT support") as there are no differences between
the boards in this respect.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>