net: pcs: xpcs: Drop redundant workqueue.h include directive

There is nothing CM workqueue-related in the driver. So the respective
include directive can be dropped.

While at it add an empty line delimiter between the generic and local path
include directives to visually separate them.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>