AArch64: Relax thumb-plt testcases regexpr.

The regexpr in these two files are a bit strict in that they don't account for
the slight changes in tags in certain arm targets which cause our address
offsets to change.   This changes the tests to allow slight movement in
locations while still strictly checking the rest.

ld/ChangeLog:

2020-08-03  Tamar Christina  <tamar.christina@arm.com>

	* testsuite/ld-arm/thumb-plt-got.d: Relax regexpr.
	* testsuite/ld-arm/thumb-plt.d: Likewise.

(cherry picked from commit 95c21066)