testsuite/arm: Add arm_hard_ok check in armv8_2-fp16-scalar-2.c

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.

2021-03-20  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* gcc.target/arm/armv8_2-fp16-scalar-2.c: Add arm_hard_ok.