ARM: dts: am437x-gp-evm: Add gp dts.

AM437x GP EVM DTS with pinmux information to make I2C on
EVM usable.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>