busybox/find-touchscreen.sh: Simplify script and recognize USB devices
Simplify the grep expression, use the more common "grep" command instead
of "egrep", avoid forking extra processes, join multiple invokations into
a single combined expression.
Change the touchscreen regex so that it also recognizes various USB
touchscreen controllers and the ad7879 i2c device.
Based on code used in OpenPLi and meta-topic.
Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl> Signed-off-by: Ross Burton <ross.burton@intel.com>
