mce, workqueue: remove keventd_up() usage

Now that workqueue can handle work item queueing from very early
during boot, there is no need to gate schedule_work() with
keventd_up().  Remove it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: linux-edac@vger.kernel.org