xf86-video-opentegra doesn't build anymore

Discovered in !565 (merged)

configure: error: Package requirements (xorg-server xproto fontsproto ) were not met:

Package dependency requirement 'libdrm >= 2.4.99' could not be satisfied.
Package 'libdrm' has version '2.4.96', required version is '>= 2.4.99'

/usr/lib/pkgconfig/dri.pc:Requires.private: libdrm >=  2.4.99

Pinging @ryang2678

The master branch of grate-driver/libdrm is at libdrm 2.4.97 so just updating to master there won't help.