[ARC] Fix ldbit test on 32-bit systems

The long immediate operand chosen for one of the ldbit tests is
equivalent to a small negative value that would fit inside an s9
operand, leading to the assembler to choose an unexpected (but
legitimate) encoding of the instruction on 32-bit systems, and
therefore causing the test to fail. This commit fixes the test by
changing the offending limm value so that it can no longer be
interpreted as an s9 operand.

gas/ChangeLog:

    * testsuite/gas/arc/nps400-6.s: Change ldbit tests so that
    limm operands are out of the range of an s9, in order to fix
    the test.
    * testsuite/gas/arc/nps400-6.d: Updated to match new expected
    output.