MFC r310612:

[evdev] Fix build for older versions of clang

There was report of stable/11 build failure on older versions of
FreeBSD. The problem was a reference to static variable in inline
function. Although fairly recent versions of clang can cope with this
situation just fine there is no strict requirement to make functions
in question inline, they're not in any time-critical codepath. So to
keep HEAD and 11-STABLE buildable on older FreeBSDs some of the util
functions were converted from inline to normal.

Reported by: hselasky