drm/amdkfd: fix mes set shader debugger process management

MES provides the driver a call to explicitly flush stale process memory
within the MES to avoid a race condition that results in a fatal
memory violation.

When SET_SHADER_DEBUGGER is called, the driver passes a memory address
that represents a process context address MES uses to keep track of
future per-process calls.

Normally, MES will purge its process context list when the last queue
has been removed.  The driver, however, can call SET_SHADER_DEBUGGER
regardless of whether a queue has been added or not.

If SET_SHADER_DEBUGGER has been called with no queues as the last call
prior to process termination, the passed process context address will
still reside within MES.

On a new process call to SET_SHADER_DEBUGGER, the driver may end up
passing an identical process context address value (based on per-process
gpu memory address) to MES but is now pointing to a new allocated buffer
object during KFD process creation.  Since the MES is unaware of this,
access of the passed address points to the stale object within MES and
triggers a fatal memory violation.

The solution is for KFD to explicitly flush the process context address
from MES on process termination.

Note that the flush call and the MES debugger calls use the same MES
interface but are separated as KFD calls to avoid conflicting with each
other.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Tested-by: Alice Wong <shiwei.wong@amd.com>
Reviewed-by: Eric Huang <jinhuieric.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>