usb: dwc2: Remove unnecessary prototypes

Remove the unnecessary prototypes for all the parameter setting
functions and declare those functions 'static' in the params.c file.

Also remove the duplicate documentation that went along with them. They
are already documented as part of the params structure definition.

Then move the constants that went along with the prototype into the
structure.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>