Currently, udev-cache system configurations are compared as shell string
variables, read into memory with the readfiles() function. This is more
complex, and significantly (27-41%) slower, than comparing them using
`cmp`. (Performance was verified on both Cortex-A9 and Intel Nehalem
systems.)
So just use cmp. This requires a few other small changes:
exclude /proc/atags from CMP_FILE_LIST if it doesn't exist to avoid
errors in `cat` and `cmp`.
`cmp -q` doesn't exist in busybox, so instead, redirect output to
/dev/null.
Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
