bsd-user/arm/target_arch_elf.h: arm get_hwcap2 impl

Implement the extended HW capabilities for HWCAP2.

Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>