arm64: dts: ti: Introduce base support for AM62x SoC

This add bare minimum DT for AM62 describing ARM compute clusters, Main,
MCU and Wakeup domain and interconnects, UARTs and I2Cs to enable
booting using ramdisk.

Hierarchy of dts files:
am62.dtsi:
base SoC skeleton which is common across am62xx family of SoCs,
includes am62-main.dtsi, am62-mcu.dtsi and am62-wakeup.dtsi
representing 3 domains and peripherals in each of these domain

am625.dtsi:
describes CPU cluster (Quad A53s). Since, am625 is a current superset
device with all peripherals, am625.dtsi includes am62.dtsi completing
SoC definition.
Individual EVMs using this SoC will just need to include am625.dtsi
thus making things easier for Board and SOM Vendors.
Future derivative SoCs will have their own am62{1-9}{1-9}.dtsi
overriding cluster / peripheral definitions with their own compatibles.

More details about the SoCs can be found in the Technical Reference Manual:
https://www.ti.com/lit/pdf/spruiv7



Co-developed-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Co-developed-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>
Link: https://lore.kernel.org/r/20220225120239.1303821-5-vigneshr@ti.com