When a PFR (or bigger reset) occurs, the device clears the VF_MBX_ARQLEN
register for all VFs. But if a VFR is triggered by a VF, the device does
NOT clear this register, and the VF driver will never see the reset.

When this happens, the VF driver will eventually timeout and attempt
recovery, and usually it will be successful. But this makes resets take
a long time and there are occasional failures.

We cannot just blithely clear this register on every reset; this has
been shown to cause synchronization problems when a PFR is triggered
with a large number of VFs.

Fix this by clearing VF_MBX_ARQLEN when the reset source is not PFR.
GlobR will trigger PFR, so this test catches that occurrence as well.
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>