usb: dwc2: Refactor register operations with clrsetbits macros

usb: dwc2: Refactor register operations with clrsetbits macros

Refactor DWC2 USB gadget driver to replace manual read-modify-write
operations with `clrsetbits_le32`, `setbits_le32`, and `clrbits_le32`
macros, which simplify the code and improve readability.

Signed-off-by: Junhui Liu <junhui.liu@pigmoral.tech>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20250126-dwc2-clrsetbits-refactor-v1-1-68c27e1b6f84@pigmoral.tech
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>