[AArch64] Use aarch64_sve_int_mode in SVE ACLE code

[AArch64] Use aarch64_sve_int_mode in SVE ACLE code

This is a like-for-like change at the moment, but is a prerequisite
for removing mode_for_int_vector.

2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-sve-builtins-functions.h
	(unary_count::expand): Use aarch64_sve_int_mode instead of
	mode_for_int_vector.

From-SVN: r278120