msm: emac: allow mii ioctls to access multiple PHYs

Allow the mii_ioctl to access multiple PHYs via the MDIO bus
when the EMAC is not connected to any external PHY. This feature
is required for fsm9900 MTP board, where the EMAC core is directly
connected to an on-board switch and the driver should support
configuring the downstream PHYs of the switch. The user space
application can use mii ioctls to configure the switch.

Change-Id: I444bbf04fbc82f5dca1aca259a404cf1be98e071
Acked-by: Jie Luo <jluo@qti.qualcomm.com>
Signed-off-by: Niranjana Vishwanathapura <nvishwan@codeaurora.org>