NVMe: Configure support for block flush

This configures an nvme request_queue as flush capable if the device
has a volatile write cache present.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index cfd084c..6266373 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -99,6 +99,7 @@
 	u32 stripe_size;
 	u16 oncs;
 	u16 abort_limit;
+	u8 vwc;
 	u8 initialized;
 };
 
diff --git a/include/uapi/linux/nvme.h b/include/uapi/linux/nvme.h
index ad9014e..f090336 100644
--- a/include/uapi/linux/nvme.h
+++ b/include/uapi/linux/nvme.h
@@ -73,6 +73,7 @@
 	NVME_CTRL_ONCS_COMPARE			= 1 << 0,
 	NVME_CTRL_ONCS_WRITE_UNCORRECTABLE	= 1 << 1,
 	NVME_CTRL_ONCS_DSM			= 1 << 2,
+	NVME_CTRL_VWC_PRESENT			= 1 << 0,
 };
 
 struct nvme_lbaf {