configure flag required to enable this: --enable-neon
Although autodetection according to __ARM_NEON would work because this
is only defined if the fpu is neon neon-fp16 neon-vfpv3 neon-vfpv4
neon-fp-armv8 crypto-neon-fp-armv8 doing that would lead to a unknown
performance impact, so it needs to be enabled manually.
Speedup is about ~1.3-1.5 on a unspecified single core Cortex A9. This
requires handling a special case for RACH with len 14 which is far too
short for neon and would actually incur a performance penalty of 25%.
Related: OS#4585
Change-Id: I58ff2cb4ce3514f43390ff0a2121f81e6a4983b5
