drm/sde: allow base layer plane stagging

Current sde driver returns warning when client
tries to setup a plane/pipe at base layer. That's
incorrect behavior. A full size base layer is
supported. This patch remove those invalid checks.

Change-Id: Id2b420c20d47aa5abbfc5558c53a16d8a011e2dc
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>