Default ashift for Amazon EC2 NVMe devices

Add a default 4 KiB ashift for Amazon EC2 NVMe devices on instances with
NVMe ephemeral devices, such as the types c5d, f1, i3 and m5d.
As per the official documentation [1] a 4096 byte blocksize should be
used to match the underlying hardware.

The string was identified via:

$ sudo sginfo -M /dev/nvme0n1
INQUIRY response (cmd: 0x12)
----------------------------
Device Type                        0
Vendor:                    NVMe
Product:                   Amazon EC2 NVMe
Revision level:

$ lsblk -io KNAME,TYPE,SIZE,MODEL
KNAME   TYPE    SIZE MODEL
nvme0n1 disk  442.4G Amazon EC2 NVMe Instance Storage

[1] https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/
    storage-optimized-instances.html
    Retrived 2018-07-03

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Troels Nørgaard <tnn@tradeshift.com>
Closes #7676

cmd/zpool/zpool_vdev.c

@@ -192,6 +192,7 @@ static vdev_disk_db_entry_t vdev_disk_database[] = {
 	{"ATA     INTEL SSDSC2BP24", 4096},
 	{"ATA     INTEL SSDSC2BP48", 4096},
 	{"NA      SmrtStorSDLKAE9W", 4096},
+	{"NVMe    Amazon EC2 NVMe ", 4096},
 	/* Imported from Open Solaris */
 	{"ATA     MARVELL SD88SA02", 4096},
 	/* Advanced format Hard drives */