hid-gfb: fix crashes on module or device removal

* add kref counting to gfb_data
* use gfb_data->virtualized to detect and handle device removal
* remove usb_active since it overlaps with virtualized
* use ENODEV as error code when device was removed
* don't release fb_bitmap twice
* fix error handling in gfb_probe
Makefile: remove explicit KVERSION from kbuild part
hid-g19: fix crash on module or device removal

* reorder cleanup sequence
* better cleanup on probe errors

Still getting crashes about sysfs attributes when removing the hid-g19
and/or the hid-ginput module while hid-gfb is in use by userspace.

These can be fixed by proper ownership of attributes by the respective
drivers (fb attributes go with hid-gfb, input attributes with hid-ginput
etc), but this breaks the current API for userspace and will be fixed
later.