aarch64: Fix matching of BRKNS

aarch64: Fix matching of BRKNS

Unlike other flag-setting SVE instructions, BRKNS sets the flags
based on an all-true governing predicate, rather than the GP operand.

gcc/
	* config/aarch64/iterators.md (SVE_BRKP): New iterator.
	* config/aarch64/aarch64-sve.md (*aarch64_brkn_cc): New pattern.
	(*aarch64_brkn_ptest): Likewise.
	(*aarch64_brk<brk_op>_cc): Restrict to SVE_BRKP.
	(*aarch64_brk<brk_op>_ptest): Likewise.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/brkn_1.c: Expect separate
	PTEST instructions.
	* gcc.target/aarch64/sve/acle/general/brkn_2.c: New test.

(cherry picked from commit 6bec66640597e2604f51fc1642c7d279164cd442)