board: ti: am571x-idk: Update pinmux for ICSS2 Ethernet

Use the same convention that was used for ICSS1 Ethernet
- If pin is output, set as PIN_OUTPUT
- If pin is input and external pull resistor present set as PIN_INPUT
- If pin is input and external pull resistor absent, set pull to same
as that of the external PHY's internall pull.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>