elf_common: update ARM ABI flag names

In the V5 ABI the flags are EF_ARM_ABI_FLOAT_HARD and
EF_ARM_ABI_FLOAT_SOFT. The flags have the same values as the legacy GCC
flags EF_ARM_VFP_FLOAT and EF_ARM_SOFT_FLOAT respectively.

The legacy names are kept for compatibility.

Reported by: Peter Smith (Linaro)
Reviewed by: imp
Sponsored by: The FreeBSD Foundation