ci: Split building of libdrm to its own script

As we are doing that in several places already and we'll need to build
in others as well.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Rohan Garg <rohan.garg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5903>
9 files changed