aarch64: Add support for unpacked SVE shifts

aarch64: Add support for unpacked SVE shifts

This patch adds support for unpacked SVE LSL, ASR and LSR.
For right shifts, the type suffix needs to be taken from the
element size rather than the container size.

gcc/
	* config/aarch64/aarch64-sve.md (<ASHIFT:optab><mode>3)
	(v<ASHIFT:optab><mode>3, @aarch64_pred_<optab><mode>)
	(*post_ra_v<ASHIFT:optab><mode>3): Extend from SVE_FULL_I to SVE_I.

gcc/testsuite/
	* gcc.target/aarch64/sve/shift_2.c: New test.