drm/amdkfd: only flush mes process context if mes support is there

Fix up on mes process context flush to prevent non-mes devices from
spamming error messages or running into undefined behaviour during
process termination.

Fixes: bd33bb14 ("drm/amdkfd: fix mes set shader debugger process management")
Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Eric Huang <jinhuieric.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>