kbuild: remove dependency on input.h from file2alias

Almost all definitions used by file2alias was already
present in mod_devicetable.h.
Added the last definition and killed the input.h usage.

The errornous include was pointed out
by: Jan Engelhardt <jengelh@linux01.gwdg.de>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Cc: Deepak Saxena <dsaxena@plexity.net>