devel/libmtdev: Update to 1.1.6

Update devel/libmtdev to 1.1.6 [0]
Switch to USES=localbase instead of manipulating CPPFLAGS [1]
Pass maintainership to x11@, since this is used in the xorg and wayland
input stacks. [0]

PR: 249962 [0], 249295 [1]
Submitted by: zeising [0]
Suggested by: daniel.engberg.lists@pyret.net [1]
Approved by: hselasky (maintainer)
Obtained from: FreeBSD Graphics Team git repo [0]