Backport from 2013-01-07 trunk r194991, r194992.

	Backport from 2013-01-07 trunk r194991, r194992.
	PR target/55897
	* doc/extend.texi (AVR Named Address Spaces): __memx goes into
	.progmemx.data now.
	* config/avr/avr.h (ADDR_SPACE_COUNT): New enum.
	(avr_addrspace_t): Add .section_name field.
	* config/avr/avr.c (progmem_section): Use ADDR_SPACE_COUNT as
	array size.
	(avr_addrspace): Same.  Initialize .section_name.  Remove last
	NULL entry.  Put __memx into .progmemx.data.
	(progmem_section_prefix): Remove.
	(avr_asm_init_sections): No need to initialize progmem_section.
	(avr_asm_named_section): Use avr_addrspace[].section_name to get
	section name prefix.
	(avr_asm_select_section): Ditto.  And use get_unnamed_section to
	retrieve the progmem section.
	* avr-c.c (avr_cpu_cpp_builtins): Use ADDR_SPACE_COUNT as loop
	boundary to run over avr_addrspace[].
	(avr_register_target_pragmas): Ditto.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_7-branch@194993 138bc75d-0d04-0410-961f-82ee72b054a4