board: ti: am571x-idk: Support 6 port Ethernet or 4 port Ethernet with LCD

The board can support either ICSS1 Ethernet ports or LCD
based on J51 jumper. Factory default is ICSS1 Ethernet ports
(i.e. Jumper not populated).

Use the GPIO to detect the jumper setting and configure the
pinmux accordingly. Also select the right DT blob based on
the chosen configuration.

J51 absent -> ICSS1 Ethernet, no LCD on VOUT -> am571x-idk.dtb
J51 present -> LCD on VOUT, no ICSS1 Ethernet -> am571x-idk-lcd-osd.dtb

At present we only support the assume it is the Legacy LCD.
LCD detection mechanism needs to be added later to differentiate
between legacy vs new LCD.

For ICSS1 Ethernet pins use the following convention to set the pinmux
as PMT data is not yet finalized.

- 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.
- Do not use SLEW_CONTROLon any pin.

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