It is currently not possible to correctly match .xt.prop information
for sections with identical VMA. Allow creation of separate property
sections in the BFD. Add assembler option --separate-prop-tables to
allow creation of separate property sections.

2018-06-04  Volodymyr Arbatov  <arbatov@cadence.com>
bfd/

	* elf32-xtensa.c (elf32xtensa_separate_props): New global
	variable.
	(xtensa_add_names): New function.
	(xtensa_property_section_name): Add new parameter
	separate_sections, use it to choose property section name.
	(xtensa_get_separate_property_section): New function.
	(xtensa_get_property_section): Invoke
	xtensa_get_separate_property_section to get individual property
	section if it exists, common property section otherwise.
	(xtensa_make_property_section): Pass elf32xtensa_separate_props
	to xtensa_property_section_name.

gas/
	* config/tc-xtensa.c (elf32xtensa_separate_props): New
	declaration.
	(option_separate_props, option_no_separate_props): New
	enumeration constants.
	(md_longopts): Add separate-prop-tables option.
	(md_parse_option): Add cases for option_separate_props and
	option_no_separate_props.
	(md_show_usage): Add help for [no-]separate-prop-tables options.