omap3evm: Update ethernet reset sequence for Rev.G board

The GPIO pin used for resetting the external LAN chip has
changed for Rev.G board.

The patch uses generic gpio API instead of direct access
to corresponding registers.

Signed-off-by: Sriramakrishnan <srk@ti.com>
Signed-off-by: Sanjeev Premi <premi@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>