MIPS: OCTEON: octeon-usb: use bitfields for control register

Code needs to compile for all platforms in order to move it to
drivers/usb/dwc3. Use Linux standard bitfield access macros
to manipulate control register.

Signed-off-by: Ladislav Michl <[email protected]>
Signed-off-by: Thomas Bogendoerfer <[email protected]>

Author: 3x380V