drm/mm: cleanup and improve next_hole_*_addr()

Skipping just one branch of the tree is not the most
effective approach.

Instead use a macro to define the traversal functions and
sort out both branch sides.

This improves the performance of the unit tests by
a factor of more than 4.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nirmoy Das <nirmoy.das@amd.com>
Link: https://patchwork.freedesktop.org/patch/370298/