aarch64: Add support for unpacked SVE MULH

aarch64: Add support for unpacked SVE MULH

This patch extends the SMULH and UMULH support to unpacked vectors.
The type suffix must be taken from the element size rather than the
container size.

The main use of these patterns is to support division and modulus
by a constant.  The conditional forms would be hard to trigger from
non-ACLE code, and ACLE code needs fully-packed vectors only.

gcc/
	* config/aarch64/aarch64-sve.md (<su>mul<mode>3_highpart)
	(@aarch64_pred_<MUL_HIGHPART:optab><mode>): Extend from SVE_FULL_I
	to SVE_I.

gcc/testsuite/
	* gcc.target/aarch64/sve/mul_highpart_3.c: New test.