board: AM335x-ICEv2: Add cpsw support

In order to enable cpsw on AM335x ICEv2 board, the following needs to be done:

1)There are few on board jumper settings which gives a choice between
cpsw and PRUSS, that needs to be properly selected[1]. Even after selecting
this, there are few GPIOs which control these muxes that needs to be held high.

2) The clock to PHY is provided by a PLL-based clock synthesizer[2] connected
via I2C. This needs to properly programmed and locked for PHY operation.
And PHY needs to be reset before before being used, which is also held by
a GPIO.

3) RMII mode needs to be selected.

[1] http://www.ti.com/lit/zip/tidr336
[2] http://www.ti.com/lit/ds/symlink/cdce913.pdf



Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>