Revert "pc: Kill the "use flash device for BIOS unless KVM" misfeature"

This reverts commit 9953f8822cc316eec9962f0a2858c3439a80adec.
While Markus's analysis is entirely correct, there are 1.6 patches
that fix the bug for real and without requiring machine type hacks.
Let's think of the children who will have to read this code, and
avoid a complicated mess of semantics that differ between <1.5,
1.5, and >1.5.

Conflicts:
	hw/i386/pc_piix.c
	hw/i386/pc_q35.c
	include/hw/i386/pc.h

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1368189483-7915-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>