The MES cached process context must be cleared on adding any queue for
the first time.

For proper debug support, the MES will clear it's cached process context
on the first call to SET_SHADER_DEBUGGER.

This allows TTMPs to be pesistently enabled in a safe manner.
Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Eric Huang <jinhuieric@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>