aarch64: Check predicate when using gen_vec_duplicate [PR98657]

aarch64: Check predicate when using gen_vec_duplicate [PR98657]

Prevents generation of a vec_duplicate with illegal predicate in
<ASHIFT:optab><mode>3.

gcc/ChangeLog:
2021-02-19  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	PR target/98657
	* config/aarch64/aarch64-sve.md (<ASHIFT:optab><mode>3): Use
	expand_vector_broadcast' to emit the vec_duplicate operand.

gcc/testsuite/ChangeLog:
2021-02-19  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	PR target/98657
	* gcc.target/aarch64/sve/pr98657.c: New test.