doc: Fix Doxyfile to skip undocumented stuff

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>
gpio: avr: Add dummy macros

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>
doc: Fix GPIO documenting

Signed-off-by: Nikita 'webconn' Maslov <wkernelteam@gmail.com>