ARM: shmobile: r8a7790: lager: add pinmux for iic0

It seems we used to rely on the default pinmux setting of this HW, but
currently we need to explicitly set the pinmux to access this bus. It is
better style, too.

Signed-off-by: Wolfram Sang <wsa@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>