Tidy up manual following review.

gcc:
	* doc/invoke.texi (ARC Options): Correct text for -mdsp-packa,
	-mxy and the -mtune options for ARC700, ARC700-xmac, ARC725D and
	ARC750D. Fix bad line-wrapping.  Spell check and correct this
	section.
	* doc/extend.texi (Declaring Attributes of Functions): Document
	use of "ilink" for ARC v2 EM.  Spell check and correct this
	section.
	(ARC Built-in Functions): Change -mEA to -mea.  Spell check and
	correct this section.