Improvements in seabios part

  * Build with distro's seabios with xen configure instead patch.
  * Use seabios 256k build instead the 128k one, because in the 128k the
    xen support will be disabled in future.
  * Removed patches no more needed:
    - debian/patches/tools-firmware-seabios-packaged.diff
  * Refreshed patches:
    - debian/patches/config-etherboot.diff
    - debian/patches/tools-firmware-etherboot-packaged.diff