powerpc/85xx: Add default usb mode and phy type to hwconfig

Move to use hwconfig for usb mode & phy type instead of magic
'usb_phy_type' environment variable on the following platforms:

MPC8536DS, P1020RDB, P1020RDB-PC, P1010RDB, P2020RDB, P2020RDB-PC,
P2020RDB, P3041DS, P4080DS, & P5020DS.

Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>