[AArch64] Pass number of units to aarch64_reverse_mask

[AArch64] Pass number of units to aarch64_reverse_mask

This patch passes the number of units to aarch64_reverse_mask,
which avoids a to_constant () once GET_MODE_NUNITS is variable.

2017-11-06  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* config/aarch64/aarch64-protos.h (aarch64_reverse_mask): Take
	the number of units too.
	* config/aarch64/aarch64.c (aarch64_reverse_mask): Likewise.
	* config/aarch64/aarch64-simd.md (vec_load_lanesoi<mode>)
	(vec_store_lanesoi<mode>, vec_load_lanesci<mode>)
	(vec_store_lanesci<mode>, vec_load_lanesxi<mode>)
	(vec_store_lanesxi<mode>): Update accordingly.

Reviewed-by: James Greenhalgh <james.greenhalgh@arm.com>
Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r254467