aarch64: Add support for unpacked SVE ASRD

aarch64: Add support for unpacked SVE ASRD

This patch adds support for both conditional and unconditional unpacked
ASRD.  This meant adding a new define_insn for the unconditional form,
instead of reusing the conditional instructions.  It also meant
extending the current conditional patterns to support merging with
any independent value, not just zero.

gcc/
	* config/aarch64/aarch64-sve.md (sdiv_pow2<mode>3): Extend from
	SVE_FULL_I to SVE_I.  Generate an UNSPEC_PRED_X.
	(*sdiv_pow2<mode>3): New pattern.
	(@cond_<sve_int_op><mode>): Extend from SVE_FULL_I to SVE_I.
	Wrap the ASRD in an UNSPEC_PRED_X.
	(*cond_<sve_int_op><mode>_2): Likewise.  Replace the UNSPEC_PRED_X
	predicate with a constant PTRUE, if it isn't already.
	(*cond_<sve_int_op><mode>_z): Replace with...
	(*cond_<sve_int_op><mode>_any): ...this new pattern.

gcc/testsuite/
	* gcc.target/aarch64/sve/asrdiv_4.c: New test.
	* gcc.target/aarch64/sve/cond_asrd_1.c: Likewise.
	* gcc.target/aarch64/sve/cond_asrd_1_run.c: Likewise.
	* gcc.target/aarch64/sve/cond_asrd_2.c: Likewise.
	* gcc.target/aarch64/sve/cond_asrd_2_run.c: Likewise.
	* gcc.target/aarch64/sve/cond_asrd_3.c: Likewise.
	* gcc.target/aarch64/sve/cond_asrd_3_run.c: Likewise.