Staging: Netlogic: Move all the netdev under single parent device

XLR has one network controller and XLS has two network controllers, each
controller has 4 gmac devices. This patch initializes each controller as
a parent device and the four gmac devices of a controller are connected
to the parent controller as a child

Signed-off-by: Ganesan Ramalingam <ganesanr@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>