* config/mips/tm-irix3.h: Clean up, use tm-bigmips.h and redefine

	* config/mips/tm-irix3.h: Clean up, use tm-bigmips.h and redefine
	the necessary bits.
	* findvar.c (value_from_register): Fix uninitialized first_addr
	which caused problems with assignment of doubles to register variables
	on some targets.
	* mipsread.c: Remove TM_FILE_OVERRIDE, include tm.h and provide the
	missing mips definitions if necessary.

	Fix handling of double register variables for mips targets and big
	endian hosts. These patches are from Paul Flinders <ptf@delcam.co.uk>.
	* config/mips/tm-mips.h: Increase MAX_REGISTER_{RAW,VIRTUAL}_SIZE to
	  8 bytes for doubles.
	* config/mips/tm-mips.h (REGISTER_CONVERT_TO_TYPE): New macro for
	  conversion of type held in multiple registers to host format.
	* config/mips/tm-mips.h (REGISTER_CONVERT_FROM_TYPE): New macro,
	  companion to REGISTER_CONVERT_TO_TYPE.
	* config/mips/tm-mips.h (EXTRACT_RETURN_VALUE, STORE_RETURN_VALUE):
	  Convert to function calls.
	* config/mips/tm-mips.h (FIX_CALL_DUMMY): New code for big endian
	  mips targets.
	* mips-tdep.c (mips_print_register): Raw buffer now needs just
	  MAX_REGISTER_RAW_SIZE bytes.
	* mips-tdep.c (mips_print_register): Use REGISTER_CONVERT_TO_TYPE
	  (if defined) for doubles.
	* mips-tdep.c: (mips_extract_return_value, mips_store_return_value):
	  New functions, take care of REGISTER_CONVERT_TO/FROM_TYPE.
	* valops.c (value_assign): Use REGISTER_CONVERT_TO_TYPE if
	  defined.
	* findvar.c (value_from_register): Use REGISTER_CONVERT_TO_TYPE if
	  defined.