We were looking for any mention of the feature name in cpuinfo, which
could have hit anything including features with common prefixes like
sme, sme2, smefa64.
Luckily this was not a problem but I'm changing this to find the
features line and split the features into a list. Then we are only
looking for exact matches.
Here's the information for one core as an example:
```
processor : 7
BogoMIPS : 200.00
Features : fp asimd evtstrm crc32 atomics fphp asimdhp cpuid <...>
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd0f
CPU revision : 0
```
(and to avoid any doubt, this is from a CPU simulated in Arm's FVP, it's
not real)
Note that the layout of the label, colon, values is sometimes aligned
but not always. So I trim whitespace a few times to normalise that.
This repeats once for each core so we only need to find one features
line.
8c122e5d3b