fstab.hikey960: make it possible for vendor partition to be remounted

as the "adb remount" checks the /vendor/etc/fstab.hikey960
file to find if the partition is a known partition,
so we need to add vendor here to make it work with adb remount.

Otherwise will get following error:
$ adb remount vendor
Unknown partition vendor, skipping
No partitions to remount
remount failed
$

Or it's not remounted to be writable after adb remount command.

Test: adb remount, and vendor partition is writable.

Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
Change-Id: I4a6e0ddc31cd62bcf9b7c42083656c7dbaed5009
diff --git a/hikey960/fstab.hikey960 b/hikey960/fstab.hikey960
index 8697004..433d31d 100644
--- a/hikey960/fstab.hikey960
+++ b/hikey960/fstab.hikey960
@@ -11,3 +11,5 @@
 /devices/platform/soc/ff37f000.dwmmc1/mmc_host/mmc*      auto       auto    defaults    voldmanaged=sdcard1:auto,encryptable=userdata
 /devices/platform/soc/ff200000.hisi_usb/ff100000.dwc3/xhci-hcd.*.auto/usb*               auto               auto      defaults  voldmanaged=usbdisk:auto,encryptable=userdata
 /devices/platform/soc/f4000000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0/nvme/nvme*      auto       auto    defaults    voldmanaged=nvmedisk:auto,encryptable=userdata
+/dev/block/by-name/system /system ext4 ro,errors=panic wait,first_stage_mount
+/dev/block/by-name/vendor /vendor ext4 ro,errors=panic wait,first_stage_mount