Always have the error injection i/f available, even if there is no
debugfs or EDAC_DEBUG enabled. We need this for testing production
kernels and environments.

Thus, the entry moves from:

 /sys/kernel/debug/edac/mc0/inject_ctrl

to:

 /sys/devices/system/edac/mc/mc0/inject_ctrl

No other changes of the interface.
Signed-off-by: Robert Richter <robert.richter@linaro.org>
Signed-off-by: Robert Richter <rric@kernel.org>