MFC r264605:
MFC r264605:

 Based on xlp_machdep.c and completed the list of options based on
 boot/mips/beri/loader/metadata.c allow FDT configuration to set
 command line options.
 This leads to an interesting quesiton of future interactions with loader.
 However for configurations without loader this allows bootverbose or boot
 single user to be set by compiling a new kernel, which is good enough for
 testing and debugging.

 Reviewed by:	rwatson
Sponsored by:	DARPA/AFRL

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