Add support for DT_MIPS_RLD_MAP_REL.

Add support for DT_MIPS_RLD_MAP_REL.

This tag allows debugging of MIPS position independent executables
and provides access to shared library information.

gdb/gdbserver/

	* linux-low.c (get_r_debug): Handle DT_MIPS_RLD_MAP_REL.

gdb/

	* solib-svr4.c (read_program_header): Add base_addr argument to
	report the runtime address of the segment.
	(find_program_interpreter): Update read_program_header call to pass
	a NULL pointer for the new argument.
	(scan_dyntag): Add ptr_addr argument to report the runtime address
	of the tag payload.
	(scan_dyntag_auxv): Likewise and use thew new base_addr argument of
	read_program_header to get the base address of the dynamic segment.
	(elf_locate_base): Update uses of scan_dyntag, scan_dyntag_auxv and
	read_program_header.
	(elf_locate_base): Scan for and handle DT_MIPS_RLD_MAP_REL.