doc: dt: net: Add fsl,wake-on-filer for eTSEC

Add the "fsl,wake-on-filer" property for eTSEC nodes to
indicate that the system has the power management
infrastructure needed to be able to wake up the system
via FGPI (filer, aka. h/w rx parser) interrupt.

Cc: Li Yang <[e-mail]>
Cc: Zhao Chenhui <[e-mail]>

Signed-off-by: Claudiu Manoil <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/fsl-tsec-phy.txt

···
     "rgmii-id", as all other connection types are detected by hardware.
   - fsl,magic-packet : If present, indicates that the hardware supports
     waking up via magic packet.
+  - fsl,wake-on-filer : If present, indicates that the hardware supports
+    waking up by Filer General Purpose Interrupt (FGPI) asserted on the
+    Rx int line.  This is an advanced power management capability allowing
+    certain packet types (user) defined by filer rules to wake up the system.
   - bd-stash : If present, indicates that the hardware supports stashing
     buffer descriptors in the L2.
   - rx-stash-len : Denotes the number of bytes of a received buffer to stash