kvm tools, bios: Make sure IRQ handlers segment is properly set

The mini bios is copied at predefined place and should have
constant segment address.

Without this patch cs value varies depending on which code
is compiled and how big bios is, it's kinda flowing error
which is not triggered yet by a pure luck.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>