arm: dts: Add support for AM62-SK

arm: dts: Add support for AM62-SK

AM62 StarterKit (SK) board is a low cost, small form factor board
designed for TI’s AM625 SoC. It supports the following interfaces:
* 2 GB DDR4 RAM
* x2 Gigabit Ethernet interfaces capable of working in Switch and MAC mode
* x1 HDMI Port with audio + x1 OLDI/LVDS Display interface for Dual Display
* x1 Headphone Jack
* x1 USB2.0 Hub with two Type A host and x1 USB Type-C DRP Port
* x1 UHS-1 capable µSD card slot
* 2.4/5 GHz WLAN + Bluetooth 4.2 through WL1837
* 512 Mbit OSPI flash
* x4 UART through UART-USB bridge
* XDS110 for onboard JTAG debug using USB
* Temperature sensors, user push buttons and LEDs
* 40-pin User Expansion Connector
* 24-pin header for peripherals in MCU island (I2C, UART, SPI, IO)
* 20-pin header for Programmable Realtime Unit (PRU) IO pins
* 15-pin CSI header

Add basic support for AM62-SK.

To keep the changes to minimum. Only UART And SD are supported at the
moment. This should serve as good example for adding new board support
based on AM62x SoC

Schematics: https://www.ti.com/lit/zip/sprr448

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>