Currently each driver specifies it's own version, and core libdrm
specifies a version. In the most common case this is fine, since there
will be exactly one libdrm installed on a system, but if there are more
than one it's possible that mesa will be linked against different
versions of libdrm. There is also the possibility that the current
approach makes the pkg-config files we generate incorrect, since there
could be #defines that use newer features if they're available.

This patch corrects all of that. All of the versions are still set by
driver (along with a default core version). Then all of the drivers that
are enabled have their versions compared and the highest version is
selected, then all libdrm checks are made with that version.

v2: - Reorder the list to have the name first and whether the dependency
      is needed second (Eric)

Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>