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 <leoli@freescale.com>
Cc: Zhao Chenhui <chenhui.zhao@freescale.com>

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>