[ARM] Fix test pr82989.c for big endian and mthumb

[ARM] Fix test pr82989.c for big endian and mthumb

The test pr82989.c which was added in one of previous commits is failing for
mthumb and big-endian configurations. The aim of this test was to check that
NEON instructions are not being used for simple shift operations. The scanning
of lsl and lsr instructions and checking its counts were just too restrictive
for different configurations. So I have now simplified the test to only check
for the absence of NEON instructions.

*** gcc/testsuite/ChangeLog ***

2018-03-21  Sudakshina Das  <sudi.das@arm.com>

	PR target/82989
	* gcc.target/arm/pr82989.c: Change dg scan-assembly directives.

From-SVN: r258723