Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

MFp4:
- Try hard to calculate a safe sp, so that the stack doesn't get smashed
while uncompressing or relocating the kernel.
- Bring in code needed to calculate the cacheline size etc, needed for
arm9_idcache_wbinv_all.

Teach the elf trampoline how to deal with gzipped kernels.

Import a small ELF trampoline, in which the kernel is embedded, and that
is able to load the kernel into memory, symbol table included. This is
needed to be able to access the symbol table from DDB without a boot
loader.