drm/amdkfd: allow compute partition mode switch with cgroup exclusions

The KFD currently bars a compute partition mode switch while a KFD
process exists.

Since cgroup excluded devices remain excluded for the lifetime of a KFD
process and user space is able to mode switch single devices, allow
users to mode switch a device with any running process that has been
cgroup excluded from this device.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Harish Kasiviswanathan <harish.kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>