pc: Make -no-fd-bootchk stick across boot order changes

pc: Make -no-fd-bootchk stick across boot order changes

Option -no-fd-bootchk asks the BIOS to attempt booting from a floppy
even when the boot sector signature isn't there, by setting a bit in
RTC CMOS.  It was added back in 2006 (commit 52ca8d6a).

Two years later, commit 0ecdffbb added monitor command boot_set.
Implemented by new function pc_boot_set().  It unconditionally clears
the floppy signature bit in CMOS.

Commit e0f084bf added -boot option once to automatically change the
boot order on first reset.  Reuses pc_boot_set(), thus also clears the
floppy signature bit.  Commit d9346e81 took care to preserve this
behavior.

Thus, -no-fd-bootchk applies to any number of boots.  Except it
applies just to the first boot with -boot once, and never after
boot_set.  Weird.  Make it stick instead: set the bit according to
-no-fd-bootchk in pc_boot_set().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1371208516-7857-6-git-send-email-armbru@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>