drm/msm/sde: fix issues in secure transition functionality

Fix mutex deadlock issues in the aspace callback functions.
Aspace callback functions are called with the mutex lock
acquired, so all the gem apis locked versions should be used
within the callbacks. Fix invalid checks in reg_dma and
modify the callback functions to reflect locked. Fix issues
with the buffer addition and removal to active_list during
secure-transition.

Change-Id: I1d22591cc751320184f5e62def2cdfe3ef87d697
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>