xtensa: allow dynamic configuration

xtensa: allow dynamic configuration

Import include/xtensa-dynconfig.h that defines XCHAL_* macros as fields
of a structure returned from the xtensa_get_config_v<x> function call.
Define that structure and fill it with default parameter values
specified in the include/xtensa-config.h.
Define reusable function xtensa_load_config that tries to load
configuration and return an address of an exported object from it.
Define functions xtensa_get_config_v{1,2} that use xtensa_load_config
to get structures xtensa_config_v{1,2}, either dynamically configured
or the default.

bfd/
	* Makefile.am (BFD32_BACKENDS, BFD32_BACKENDS_CFILES): Append
	xtensa-dynconfig.c.
	* Makefile.in: Regenerate.
	* configure: Regenerate.
	* configure.ac (xtensa_elf32_be_vec, xtensa_elf32_le_vec): Add
	xtensa-dynconfig.lo to the tb.
	* elf32-xtensa.c (xtensa-config.h): Replace #include with
	xtensa-dynconfig.h.
	(XSHAL_ABI, XTHAL_ABI_WINDOWED, XTHAL_ABI_CALL0): Remove
	definitions.
	* xtensa-dynconfig.c: New file.
	* xtensa-isa.c (xtensa-dynconfig.h): New #include.
	(xtensa_get_modules): New function.
	(xtensa_isa_init): Call xtensa_get_modules instead of taking
	address of global xtensa_modules.

gas/
	* config/tc-xtensa.c (xtensa-config.h): Replace #include with
	xtensa-dynconfig.h.
	(XTHAL_ABI_WINDOWED, XTHAL_ABI_CALL0, XTENSA_MARCH_EARLIEST):
	Remove definitions.
	* config/tc-xtensa.h (xtensa-config.h): Replace #include with
	xtensa-dynconfig.h.
	* config/xtensa-relax.c (xtensa-config.h): Replace #include with
	xtensa-dynconfig.h.
	(XCHAL_HAVE_WIDE_BRANCHES): Remove definition.

include/
	* xtensa-dynconfig.h: New file.

ld/
	* emultempl/xtensaelf.em (xtensa-config.h): Replace #include
	with xtensa-dynconfig.h.
	(XTHAL_ABI_WINDOWED, XTHAL_ABI_CALL0): Remove definitions.