drm/msm: Fix drm_mm bottom_up search

The bottom up search of drm_mm hole nodes is
currently broken. It does not correctly look
for the first hole (smallest address) that fits
the allocation from the bottom up. Use an RB tree
to record hole nodes with their address as key,
so that the hole with the smallest address that
satisfies the request can be looked up.

Change-Id: Ie3020cb4e8b6db13a35d0fe5caaa8781cb6ced9f
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>