drm/amdgpu: add debugfs node to toggle ras error cnt harvest

Before ras recovery is issued, user could operate this debugfs
node to enable/disable the harvest of all RAS IPs' ras error
count registers, which will help keep hardware's registers'
status instead of cleaning up them.

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Dennis Li <Dennis.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>