board: ti: am57xx: Add support for the am571x idk

board: ti: am57xx: Add support for the am571x idk

The AM571x Industrial Development Kit (IDK) is a board based on TI's
AM571x SoC which has a single core 1.5GHz Cortex-A15processor. This
board is a development platform for the Industrial Market with:

- 1GB of DDR3L
- Dual 1Gbps Ethernet
- HDMI
- PRU-ICSS
- uSD
- 16GB eMMC
- CAN
- RS-485
- PCIe
- USB3.0
- Video Input Port
- Industrial IO port and expansion connector

The PRU/ICSS will be supported by 3rd party software for EtherCat,
Profibus, and other Industrial protocols.

The link to the data sheet and TRM can be found here:
http://www.ti.com/product/AM5718

Signed-off-by: Steve Kipisz <[email protected]>
Signed-off-by: Nishanth Menon <[email protected]>
Signed-off-by: Lokesh Vutla <[email protected]>
Reviewed-by: Tom Rini <[email protected]>