SO3 v6.1.0

SO3 6.1.0 is the last stable release before the move to the Infrabase (BitBake)
build system in 6.2.0. It gathers ~4.5 years of work since v2021_4_0
(Jan 2021), the headline being first-class integration with the AVZ
hypervisor and the SOO capsule paradigm.

Virtualization — AVZ & SOO

• Adaptation of SO3 to run as a guest on the AVZ hypervisor, and AVZ
  configuration/build integration into the SO3 tree.
• The SOO capsule paradigm (replacing the former Mobile Entity / ME):
  SO3 capsules injected and managed at runtime, with the vbus/vbstore
  back/front virtual driver model (vuart, vlogs, …).
• Hooks to support Portainer-driven tasks on top of AVZ.

Graphics & user space

• LVGL updated to v9.3, with demo, performance-test and benchmark
  applications; framebuffer support on QEMU virt.
• New init / shell program and user-space improvements.
• C library additions: setjmp / longjmp, clock support, earlier
  gettimeofday() / clock_gettime().

System & platforms

• Robustness fixes in MMU configuration, cache handling (notably Cortex-A72),
  spinlock alignment on aarch64, VFS and process/frame-table management.
• Device model, FDT parsing and initcall improvements carried forward.
• Targets: QEMU virt32 / virt64, Raspberry Pi 4 (incl. Sense-HAT).
• New version scheme (leading to the 6.x numbering).

Tooling

• CI / Docker images for LVGL performance testing; clang-format style
  enforcement.

Full changelog: v2021_4_0...v6.1.0