libm: use neon optimized sin/cos/pow/sqrt/sqrtf

This enables the optimized functions for all devices that
support the NEON instruction set.

benchmark       iterations  Normal ns/op  NEON ns/op
BM_math_sin       10000000  126           109
BM_math_cos       10000000  112           114
BM_math_pow        5000000  375           328
BM_math_sqrt      50000000  496            38
BM_math_sqrtf    100000000  136            25

Change-Id: I2b2ee9ab1769c994edac4a5e56eee2fafa4a37a7
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>