The Flash memory chip used on the SVEC is obsolete. The new one has a different ID
and sector size. Update the svec-flasher tool to work with both type of memories.

Also update documentation accordingly.

See also:
https://www.ohwr.org/project/svec/issues/19
https://forums.ohwr.org/t/wrtd-installation-instructions/848300/11Signed-off-by: Dimitris Lampridis <dimitris.lampridis@cern.ch>