Document usb - #41

This PR enhances the documentation for the usb.h file using Doxygen, ensuring comprehensive coverage of all elements, including functions, macros, and enums. The documentation now provides clear descriptions of the purpose, usage, and return values for each function, as well as detailed information on the USB state enum and the oslGetUsbState macro.

Key Updates:

• File Overview: Added a @file tag to provide a brief overview of the usb.h file's purpose.
• Function Documentation: Each USB function (oslInitUsbStorage, oslStartUsbStorage, oslStopUsbStorage, and oslDeinitUsbStorage) is now fully documented, with clear descriptions and return values.
• Enum Documentation: Documented the USB state enum, explaining the different possible states of the USB connection.
• Macro Documentation: The oslGetUsbState macro has been documented to clarify its function.
• Grouping: Grouped all USB-related functions under the "Usb" module using the @defgroup tag for better organization in the generated documentation.

This update improves code readability and helps future developers understand the USB module's functions and usage more effectively.