staging: gpib: Add user api include files

User api include files used by drivers and userland code.
The files are also distributed with the userland package.
Since these include files have been used by many applications we
had to keep the camelCase enums, typedefs and uint8_t declarations.

Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20240918121908.19366-5-dpenkler@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>