The current chipid params comparison code is based on a simple
memcmp. This doesn't work since the structure contains a string
pointer. Replace it with a simple field-by-field comparison.

The chipid configuration parser currently emits a warning when it
encounters a file with the flash type set to
STLINK_FLASH_TYPE_UNKNOWN. In practice, this means that the warning
will always be printed since 'unknown_device.chip' uses this
value. Make STLINK_FLASH_TYPE_UNKNOWN a permitted value in the config
file parser.

Co-authored-by: Grzegorz Szymaszek <gszymaszek@short.pl>