mach-o cleanup: remove useless calls to bfd_seek.

mach-o cleanup: remove useless calls to bfd_seek.

Also support new commands.

bfd/
	* mach-o.h (struct mach_o_data_struct): Add hdr_offset field.
	(bfd_mach_o_fat_archive_p): Renames prototype.
	(bfd_mach_o_fat_openr_next_archived_file): Renames.
	(bfd_mach_o_header_p): Add argument.
	* mach-o.c (bfd_mach_o_read_header): Add hdr_off argument and
	use it.
	(bfd_mach_o_read_section_32, bfd_mach_o_read_section_64)
	(bfd_mach_o_read_section): Remove offset argument.
	(bfd_mach_o_read_dylinker): Remove bfd_seek call.
	(bfd_mach_o_read_dylib, bfd_mach_o_read_prebound_dylib)
	(bfd_mach_o_read_prebind_cksum, bfd_mach_o_read_twolevel_hints)
	(bfd_mach_o_read_fvmlib, bfd_mach_o_read_dysymtab)
	(bfd_mach_o_read_symtab, bfd_mach_o_read_uuid)
	(bfd_mach_o_read_linkedit, bfd_mach_o_read_str)
	(bfd_mach_o_read_dyld_info, bfd_mach_o_read_version_min)
	(bfd_mach_o_read_encryption_info): Likewise.
	(bfd_mach_o_read_encryption_info_64): New function.
	(bfd_mach_o_read_main, bfd_mach_o_read_source_version)
	(bfd_mach_o_read_segment): Remove call to bfd_seek.
	(bfd_mach_o_read_command): Use hdr_offset in bfd_seek.
	Handle BFD_MACH_O_LC_LINKER_OPTIMIZATION_HINT,
	BFD_MACH_O_LC_ENCRYPTION_INFO_64, BFD_MACH_O_LC_VERSION_MIN_WATCHOS.
	(bfd_mach_o_header_p): Add hdr_off argument.
	(bfd_mach_o_gen_object_p, bfd_mach_o_gen_core_p): Adjust calls.
	(bfd_mach_o_fat_archive_p): Renames.
	(bfd_mach_o_fat_openr_next_archived_file): Renames.
	(bfd_mach_o_close_and_cleanup): Remove useless code.
	(bfd_mach_o_close_and_cleanup): Define.
	* mach-o-x86-64.c (bfd_mach_o_x86_64_object_p)
	(bfd_mach_o_x86_64_core_p): Adjust calls.
	* mach-o-target.c: Move defines for archive from mach-o.c.
	Remove check on TARGET_ARCHIVE.
	* mach-o-i386.c (bfd_mach_o_i386_object_p)
	(bfd_mach_o_i386_core_p): Adjust calls.