seoul: update branch to using vbios emulators

* use seoul branch containing vbios emulator

* report the memory model in the VBE mode info as otherwise the
  Genode framebuffer driver will ignore this mode

Fixes #1261
iso9660: remove on-demand paging

Required to run a Genode VM provided as ISO - issue #1261
ahci: ignore spurious interrupts

Qemu 2.0 makes trouble when using seoul-disc.run - related to #1261
seoul: add script turning Genode scenario into VM

Related to issue #1261