new "stellaris recover" command

new "stellaris recover" command

Stellaris chips have a procedure for restoring the chip to
what's effectively the "as-manufactured" state, with all the
non-volatile memory erased.  That includes all flash memory,
plus things like the flash protection bits and various control
words which can for example disable debugger access.  clearly,
this can be useful during development.

Luminary/TI provides an MS-Windows utility to perform this
procedure along with its Stellaris developer kits.  Now OpenOCD
users will no longer need to use that MS-Windows utility.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>