drm/msm/sde: add support to attach/detach context banks

This change adds API to attach detach the context. This change is
required for secure display and secure camera preview use cases.
The APIs provide support to attach/detach all contexts or only
secure contexts.

CRs-Fixed: 2064272
Change-Id: Ie6784920df4e03f1dafce54e22e2996923c01054
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>