vgabios: Make sure exported structs use PACKED.

vgabios: Make sure exported structs use PACKED.

Commit ca668640 introduced structs for data returned from the
handle_101b and handle_101c calls.  However, the structs were not
declared as packed and that caused incorrect behavior for
handle_101b.  This was seen to break some old DOS programs (Win3 setup
and DISPLAY.SYS).  This patch adds in the necessary PACKED declaration
to the structs.

The 'struct saveBDAstate' remains un-packed, as it does not appear
that its contents are documented.  (And, its format already differs
from what was in the previous "lgpl vgabios".)

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>