disp: msm: refactor dma buf attach device assignment

Assign default drm device for dma buf_attach when
IOMMMU is not present and for stage-2 only buffers.
Avoid setting lazy_unmap for stage-2 only buffers as
it doesn't have any impact without nested translations.
Assign default drm device when no device is found to
support transitions between secure usecases where
the nested context banks might not be attached back
at the prime_fd_to_handle time. These buffers would
be attached with the correct context bank device
during the delayed_import.

Change-Id: I9ccb38876d7843b4411762c7b8006ae8fca85391
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>