platform/mulle: Add tool for finding specific tty.

Searches all attached FT2232H devices and compares their serial numbers
with the given serial numbers, if it finds one, print its tty name.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
platform/mulle: Find tty name via programmer serial number.

Use find-tty.sh to find the correct tty if PROGRAMMER_SERIAL is defined.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>