arm64: dts: ti: Add Support for AM654 SoC

The AM654 SoC is a lead device of the K3 Multicore SoC architecture
platform, targeted for broad market and industrial control with aim to
meet the complex processing needs of modern embedded products.

Some highlights of this SoC are:
* Quad ARMv8 A53 cores split over two clusters
* GICv3 compliant GIC500
* Configurable L3 Cache and IO-coherent architecture
* Dual lock-step capable R5F uC for safety-critical applications
* High data throughput capable distributed DMA architecture under NAVSS
* Three Gigabit Industrial Communication Subsystems (ICSSG), each with dual
  PRUs and dual RTUs
* Hardware accelerator block containing AES/DES/SHA/MD5 called SA2UL
* Centralized System Controller for Security, Power, and Resource
  management.
* Dual ADCSS, eQEP/eCAP, eHRPWM, dual CAN-FD
* Flash subsystem with OSPI and Hyperbus interfaces
* Multimedia capability with CAL, DSS7-UL, SGX544, McASP
* Peripheral connectivity including USB3, PCIE, MMC/SD, GPMC, I2C, SPI,
  GPIO

See AM65x Technical Reference Manual (SPRUID7, April 2018)
for further details: http://www.ti.com/lit/pdf/spruid7

NOTE:
1. AM654 is the first of the device variants, hence we introduce a
   generic am65.dtsi.
2. We indicate the proper bus topology, the ranges are elaborated in
   each bus segment instead of using the top level ranges to make sure
   that peripherals in each segment use the address space accurately.
3. Peripherals in each bus segment is maintained in a separate dtsi
   allowing for reuse in different bus segment representation from a
   different core such as R5. This is also the reason for maintaining a
   1-1 address map in the ranges.
4. Cache descriptions follow the ARM64 standard description.

Further tweaks may be necessary as we introduce more complex devices,
but can be introduced in context of the device introduction.

Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Benjamin Fair <b-fair@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>