[AArch64] Move code around

[AArch64] Move code around

This patch simply moves code around, in order to make the later
patches easier to read, and to avoid forward declarations.
It doesn't add the missing function comments because the interfaces
will change in a later patch.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* config/aarch64/aarch64.c (aarch64_add_constant_internal)
	(aarch64_add_constant, aarch64_add_sp, aarch64_sub_sp): Move
	earlier in file.

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: r254325