[ARM] libm: reimplement a few fp functions

Summary:
This has been re-implemented and only supports
neon devices due to neon instructions in use. Sqrt(f)
functions are more accuracy forgiving with two neon
mov instructions

s_fmal was included in this change due to needing a bit of
extra work even though Android currently treats long doubles
as doubles. For this reason, s_fmal is currently unused.

Instead of using bsd style aliasing for fmal in fma, _fmal is
defined by s_fmal.S, then s_fma.S is inherited with a matching
ENTRY and END.

Reviewers: randall.rushing, synergy

Reviewed By: synergy

CC: anders3408

Differential Revision: http://review.codefirex.com/D504