Support Mips architecture

Support Mips architecture

	* backends/Makefile.am (modules): Add mips.
	(mips_SRCS): New var for mips_init.c mips_symbol.c.
	(libebl_backends_a_SOURCES): Add mips_SRCS.
	* backends/mips_init.c: New file.
	* backends/mips_reloc.def: Likewise.
	* backends/mips_symbol.c: Likewise.
	* libebl/eblopenbackend.c (mips_init): Declare.
	(machines): Add mips.
	* libelf/libelfP.h: Add ELF64_MIPS_R_TYPE{1,2,3}

Signed-off-by: Ying Huang <ying.huang@oss.cipunited.com>