drivers: udc_dwc2: Inline vendor quirks if possible

Constify vendor quirks structure to not keep it in RAM. Use constified
vendor quirks structure directly if there is only one snps,dwc2 instance
to allow compiler inlining quirk implementation.

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>
Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>