rockchip-wic.inc: don't let wic edit fstab

For a while we've noticed that /etc/fstab ends up with "junk" appended to the
end e.g.:

	/dev/sda1       loader1 vfat    defaults        0       0
	/dev/sda2       reserved1       vfat    defaults        0       0
	/dev/sda3       reserved2       vfat    defaults        0       0
	/dev/sda4       loader2 vfat    defaults        0       0
	/dev/sda5       atf     vfat    defaults        0       0
	/dev/sda6       /boot   vfat    defaults        0       0

In most cases this doesn't appear to affect the systems negatively.
However, with the recent patch to switch to UUIDs [0aa5e600: "use uuid
instead of hard-coding root device"] this started becoming an issue on systems
using systemd. Therefore we need to stop wic from adding these junk entries so
that systems continue to boot correctly.

Build tested with core-image-base, nodistro, with both sysvinit and systemd
for:
- marsboard-rk3066
- rock2-square
- firefly-rk3288
- vyasa-rk3288
- nanopi-m4[-2gb]
- tinker-board[-s]
- rock-pi-e
- rock-pi-4[abc]
- rock64

Run tested, core-image-base, both sysvinit and systemd on:
- tinker-board
- rock-pi-e
- rock-pi-4b
- rock64

Commit message updated by Trevor Woerner <twoerner@gmail.com>

Tested-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: MarkusVolk <f_l_k@t-online.de>

conf/machine/include/rockchip-wic.inc

@@ -26,3 +26,6 @@ WICVARS:append = " \
 	SPL_BINARY \
 	UBOOT_SUFFIX \
 	"
+
+# Do not update fstab file while creating wic images
+WIC_CREATE_EXTRA_ARGS ?= "--no-fstab-update"