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

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

MFC r233230, r233323:

Improve device tree blob (DTB) handling in loader(8).

Enable using the statically embedded blob from the kernel, if present. The
KLD loaded DTB takes precedence, but they are both recognized and handled in
the same way.

Improve FDT handling in loader(8) and make it more robust.

o Fix buffer overflows when using a long property body in node paths.
o Fix loop end condition when iterating through the symbol table.
o Better error handling during node modification, better problem reporting.
o Eliminate build time warnings.

Submitted by: Lukasz Wojcik
Obtained from: Semihalf

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

Approved by: re (implicit)

Initial loader(8) support for Flattened Device Tree.

o This is disabled by default for now, and can be enabled using WITH_FDT at
build time.

o Tested with ARM and PowerPC.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation