elfdump: Improve section type reporting

The SHT range 0x70000000-0x7fffffff is processor-specific.  Pass the
ELF machine type header to sh_types so the section header type name can
be reported correctly for the given processor.

For all ranges report the actual value for unknown types.

Add MIPS-specific type SHT_MIPS_OPTIONS.

CR:		D483
Reviewed by:	sbruno, marcel
Sponsored by:	DARPA, AFRL