testsuite/arm: Add arm_hard_ok check in armv8_2-fp16-scalar-2.c
This test relies on -mfloat-abi=hard to pass (otherwise
test_mov_imm_[12] directly build the 1.0 fp16 representation via movw
r0, #15360 rather than using vmov.f16 s0, #1.0e+0 as expected by
scan-assembler-times)
Adding the arm_hard_ok check makes the test unsupported eg. on
arm-linux-gnueabi instead of reporting a failure.