dediprog: Revise prefix check for given programmer id

The SF600Plus-G2 uses a new prefix `S6B' for the serial number. Refactor
the code to ease more prefix additions and add this one.

Change-Id: I10a57446041352e391462a3bef42f570720a8d50
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/105
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
1 file changed