rs6000: Simplify "switch (which_alternative)" patterns

rs6000: Simplify "switch (which_alternative)" patterns

A few of the rs6000 patterns use C code as output control string, where
that code is just a "switch (which_alternative)" with all alternatives
returning a constant string or just the result of a function call as
template.
Write such cases as just a list of templates, with the few pieces that
are C code preceded by "*".

	* config/rs6000/altivec.md (*altivec_mov<mode>): Write the output
	control string as a list of templates instead of as C code.
	(*altivec_movti): Ditto.
	* config/rs6000/darwin.md (movdf_low_di): Ditto.

From-SVN: r264587