Move utility macro from XKBcommonint.h to utils.h

Move utility macro from XKBcommonint.h to utils.h

And merge all the similar ones into the same name.
The u* prefix is chosen over the _Xkb prefix because it has more uses
throughout the codebase. But It should now be simple to choose a nice
prefix and stay consistent.

Signed-off-by: Ran Benita <ran234@gmail.com>
[daniels: fixed for the case where we have strcasecmp]