rs6000: optimize moving to sf from highpart di

rs6000: optimize moving to sf from highpart di

Currently, we have the pattern "movsf_from_si2" which was trying
to support moving high part DI to SF.

But current pattern only accepts "ashiftrt":
XX:SF=bitcast:SF(subreg(YY:DI>>32),0), but actually "lshiftrt" should
also be ok.
And current pattern only supports BE.

Here, updating the pattern to support BE and "lshiftrt".

	PR target/108338

gcc/ChangeLog:

	* config/rs6000/predicates.md (lowpart_subreg_operator): New
	define_predicate.
	* config/rs6000/rs6000.md (any_rshift): New code_iterator.
	(movsf_from_si2): Rename to ...
	(movsf_from_si2_<code>): ... this.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pr108338.c: New test.