[AArch64] Add const_offset field to aarch64_address_info

[AArch64] Add const_offset field to aarch64_address_info

This patch records the integer value of the address offset in
aarch64_address_info, so that it doesn't need to be re-extracted
from the rtx.  The SVE port will make more use of this.  The patch
also uses poly_int64 routines to manipulate the offset, rather than
just handling CONST_INTs.

2018-01-11  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* config/aarch64/aarch64.c (aarch64_address_info): Add a const_offset
	field.
	(aarch64_classify_address): Initialize it.  Track polynomial offsets.
	(aarch64_print_address_internal): Use it to check for a zero offset.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r256534