bitwise operation between different enumeration types

mips.cc:9478:50: error: bitwise operation between different enumeration types ‘elfcpp::<unnamed enum>’ and ‘elfcpp::<unnamed enum>’ is deprecated [-Werror=deprecated-enum-enum-conversion]
 9478 |           merged_flags &= ~(elfcpp::EF_MIPS_ARCH | elfcpp::EF_MIPS_MACH);
      |                             ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

	* mips.h: Define all the EF_MIPS values in one enum.