Start implementing struct flashprog_programmer

Our libflashprog API was already prepared for a programmer level context
stored in an opaque `struct flashprog_programmer`. We start filling this
struct with a pointer to the programmer driver (entry in the programmer
table) and a mutable copy of the parameter string.

Change-Id: If9a795627b1e50ea6006569e723f400ff337be20
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/72525
4 files changed