graphics/libdrm: Update to 2.4.96
Rework local patches a bit because of upstream changes.
Changelog:
https://lists.freedesktop.org/archives/dri-devel/2018-August/187286.html
https://lists.x.org/archives/xorg-announce/2018-October/002920.html
https://lists.x.org/archives/xorg-announce/2018-October/002925.html
PR: 231607
Submitted by: voidanix (original version)
Obtained from: https://github.com/FreeBSDDesktop/freebsd-ports/tree/feature/libdrm