ld/aarch64: xfail non-PIC shared object tests on aarch64

aarch64 does not support building non-PIC shared objects, so mark
tests for these as xfail.

ld/testsuite/ChangeLog:

2014-05-20  Will Newton  <will.newton@linaro.org>

	* ld-shared/shared.exp: Mark non-PIC shared object tests
	as xfail on aarch64.