qoriq/p1_p2_rdb_pc: USB device-tree fixups for P1020
Resolve P1020 second USB controller multiplexing with eLBC
- mandatory to mention USB2 in hwconfig string to select it
over eLBC, otherwise USB2 node is removed
- works only for SPI and SD boot
Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com> Signed-off-by: Kumar Gala <galak@kernel.crashing.org> Signed-off-by: Zhicheng Fan <B32736@freescale.com> Signed-off-by: Andy Fleming <afleming@freescale.com>