mips.exp: Comment !CPU in the isa* pseudo-options.

	* gcc.target/mips/mips.exp: Comment !CPU in the isa* pseudo-options.
	(mips-dg-options): When matching isa* pseudo-options make
	'value' optional and accept ! entries.  Use $spec instead of
	$isa_spec in the isa pseudo-option error message.  Only
	perform the ISA-range check when 'value' is set.  If arch is
	matching any CPU in the ! entries switch to its generic ISA.
	* gcc.target/mips/branch-1.c: Pass isa=!octeon.
	* gcc.target/mips/dmult-1.c: Pass isa=64!octeon rather than
	-mips64.

From-SVN: r144306