drm/amdgpu: refine reboot debugfs operation in ras case (v3)

Ras reboot debugfs node allows user one easy control to avoid
gpu recovery hang problem and directly reboot system per card
basis, after ras uncorrectable error happens. However, it is
one common entry, which should get rid of ras_ctrl node and
remove ip dependence when inputting by user. So add one new
auto_reboot node in ras debugfs dir to achieve this.

v2: in commit mssage, add justification why ras reboot debugfs
node is needed.
v3: use debugfs_create_bool to create debugfs file for boolean value

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>