[AArch64] Fix constraints for CPY /M

[AArch64] Fix constraints for CPY /M

The constraints for CPY /M allowed p0-p15 instead of the intended p0-p7.
This looks like a pasto from the preceding constant pattern, where p0-p15
is allowed.

2020-01-06  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-sve.md (@aarch64_sel_dup<mode>): Use Upl
	rather than Upa for CPY /M.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/cpy_1.c: New test.

From-SVN: r279899