ice: support optional flags in signature segment header

An optional flag field has been added to the signature segment header.
The field contains two flags, a "valid" bit, and a "last segment" bit
that indicates whether the segment is the last segment that will be
sent to firmware.

If the flag field's valid bit is NOT set, then as was done before,
assume that this is the last segment being downloaded.

However, if the flag field's valid bit IS set, then use the last segment
flag to determine if this segment is the last segment to download.

Signed-off-by: Paul Greenwalt <paul.greenwalt@intel.com>
Signed-off-by: Ahmed Zaki <ahmed.zaki@intel.com>
Co-developed-by: Dan Nowlin <dan.nowlin@intel.com>
Signed-off-by: Dan Nowlin <dan.nowlin@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>