drm/msm/sde: unmap buffers when context is detached

When a context bank is detached all the gem objects iova
becomes invalid, so there is need to unmap all the gem objects.
After attach of the context bank, the buffers can be mapped again
properly. This change adds support of maintaining an active list
for the address space and unmaps the buffers when the domain is
detached. Before unmapping the buffers all the clients need to
be informed that detach is pending or reattach has happened so
that they can take necessary steps before the domain change
condition.
This change is required for switching between secure and non
secure state in Secure display and secure camera use case.

CRs-Fixed: 2064272
Change-Id: I33022e15a369ac7d42b7965d97b4b14d86e6b0fa
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>