Fix libdrm to accurately report if kms is available

[rezny]

Summary

For reasons unknown, we had a patch in libdrm that made it report kms is always available. That patch is the reason the Intel DDX is not loading the kms driver automatically; it thinks the driver is alreday loaded so it doesn't try. There is similar logic in the ATI driver, but we have a patch adding an unconditional kldload("radeonkms") to compensate, which should be possible to drop after this useless patch is dropped from libdrm.

Test Plan

Poudriere 10.3/11.0 amd64/i386 OK, run tested on 11 amd64 to verify Intel DXX now loads i915kms automatically as expected

[swills]

Approved