USB: mos7720: rename registers

Some of the register names defined here are matching with registers
defined in other places. Like DCR is defined here and DCR is also
a register in mn10300 architecture. So when we are building this with
mn10300, build fails.
To avoid we rename all the registers.
Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Johan Hovold <johan@kernel.org>