Float16: Fix test failures for non ELF targets

Float16: Fix test failures for non ELF targets

The tests were failing due to md_atof trying to do word-wise endian
switching on the float16 (for little-endian targets sometimes
multi word values have their word order changed).
However since a float16 is only 1 word wide, it would end up writing
incorrect data, as you cannot switch the word order of just one word.

	* config/tc-arm.c (md_atof): Add precision check.  Formatting.