EDAC: Rework workqueue handling

Hide the EDAC workqueue pointer in a separate compilation unit and add
accessors for the workqueue manipulations needed.

Remove edac_pci_reset_delay_period() which wasn't used by anything. It
seems it got added without a user with

  91b99041c1d5 ("drivers/edac: updated PCI monitoring")

Signed-off-by: Borislav Petkov <bp@suse.de>
diff --git a/drivers/edac/Makefile b/drivers/edac/Makefile
index dbf53e0..be163e2 100644
--- a/drivers/edac/Makefile
+++ b/drivers/edac/Makefile
@@ -10,7 +10,7 @@
 obj-$(CONFIG_EDAC_MM_EDAC)		+= edac_core.o
 
 edac_core-y	:= edac_mc.o edac_device.o edac_mc_sysfs.o
-edac_core-y	+= edac_module.o edac_device_sysfs.o
+edac_core-y	+= edac_module.o edac_device_sysfs.o wq.o
 
 edac_core-$(CONFIG_EDAC_DEBUG)		+= debugfs.o