arm64: dts: ti: k3-am65: Add MSMC RAM node

The AM65 SoC has 2MB MSMC RAM. Add this as a mmio-sram
node so drivers can use it via genpool API.

Following areas are marked reserved:
- Lower 128KB for ATF
- 64KB@0xf0000 for SYSFW
- Upper 1MB for cache

The reserved locations are subject to change at runtime by
the bootloader.

Cc: Nishanth Menon <nm@ti.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Andrew F. Davis <afd@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>