nvme: split pci module out of core module

NVMe over Fabrics drivers are going to reuse the core,
so splits nvme.ko into 2 modules:

nvme-core.ko: the core part
nvme.ko: the PCI driver

Export symbols from nvme-core.ko.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/nvme/host/Makefile b/drivers/nvme/host/Makefile
index 51bf908..9a3ca89 100644
--- a/drivers/nvme/host/Makefile
+++ b/drivers/nvme/host/Makefile
@@ -1,6 +1,8 @@
+obj-$(CONFIG_NVME_CORE)			+= nvme-core.o
+obj-$(CONFIG_BLK_DEV_NVME)		+= nvme.o
 
-obj-$(CONFIG_BLK_DEV_NVME)     += nvme.o
+nvme-core-y				:= core.o
+nvme-core-$(CONFIG_BLK_DEV_NVME_SCSI)	+= scsi.o
+nvme-core-$(CONFIG_NVM)			+= lightnvm.o
 
-lightnvm-$(CONFIG_NVM)			:= lightnvm.o
-nvme-y					+= core.o pci.o $(lightnvm-y)
-nvme-$(CONFIG_BLK_DEV_NVME_SCSI)        += scsi.o
+nvme-y					+= pci.o