vfio/xe: Notify PF about VF FLR in reset_prepare

vfio/xe: Notify PF about VF FLR in reset_prepare

Hook into the PCI error handler reset_prepare() callback to notify
the PF about an upcoming VF FLR before reset_done() is executed.
This enables early FLR_PREPARE signaling and ensures that the PF is
aware of the reset before the completion wait begins.

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Alex Williamson <alex@shazbot.org>
Link: https://patch.msgid.link/20260309152449.910636-3-piotr.piorkowski@intel.com
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>