testsuite/arm: Add arm_v8_2a_fp16_neon and arm_v8_2a_bf16_neon options

testsuite/arm: Add arm_v8_2a_fp16_neon and arm_v8_2a_bf16_neon options

A few tests lack the dg-add-options directives associated with the
dg-require-effective-target they are using. Adding them enables to
pass the right float-abi option, and thus make the tests pass instead
of emit an error.

For instance, we now pass -mfloat-abi=softfp on arm-linux-gnueabi
targets and the tests pass.

2021-03-19  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* gcc.target/arm/bfloat16_scalar_typecheck.c: Add
	arm_v8_2a_fp16_neon and arm_v8_2a_bf16_neon.
	* gcc.target/arm/bfloat16_vector_typecheck_1.c: Likewise.
	* gcc.target/arm/bfloat16_vector_typecheck_2.c: Likewise.