ARM: OMAP4/5: Centralize gpi2c_init

Centralize gpi2c_init into omap_common from the sys_proto header so
that the information can be reused across SoCs.

Signed-off-by: Steve Kipisz <s-kipisz2@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>