linux-yocto: introduce 6.16 reference kernels

linux-yocto: introduce 6.16 reference kernels

Adding the 6.16 reference kernels as our latest reference for
the fall 2025 release.

This has been tested against:

  - x86, x86-64
  - ppc
  - mips, mips64
  - arm, arm64
  - riscv32, riscv64

The -standard, -rt and -tiny variantes have been validated.

For various iamges. All testing done under qemu, hardware
references will follow later.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>