graphics/drm-legacy-kmod: fix build

[pkubaj]

Summary

Fix compilation, sys/dev/drm was removed from base.

Also fix runtime issues on powerpc64

[jmd]

Approved with the exception of the patch file - please submit that to our upstream repository. I do not want the port to diverge from that.

Once you've done that, update hash and version in port and feel free to commit with my approval. Thanks!

[pkubaj]

https://github.com/FreeBSDDesktop/drm-legacy/pull/8

[pkubaj]

Already in ports.

[pkubaj]

It still doesn't install:

===>   Registering installation for drm-legacy-kmod-g20190523
pkg-static: Unable to access file /tmp/usr/ports/graphics/drm-legacy-kmod/work/stage/boot/modules/i915kms.ko:No such file or directory
*** Error code 74

i915kms is not available on powerpc64.

[linimon]

My testing also showed that these two changes are still needed.

[jmd]

Thanks, feel free to land!