[ImageBuilder] Add 'bootz' to a list of supported boot commands

[Michal Orzel <michal.orzel@xxxxxxx>]

At the moment, in order to boot 32-bit images, we need to set BOOT_CMD
to 'bootm' which results in adding a u-boot header on top of an image.
Add 'bootz' to a list of supported boot commands, so that we can skip
this extra step. In most cases, specifying 'bootm' should only be needed
for images without Linux kernel Image/zImage header. Otherwise, we can
use 'booti'/'bootz'.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 README.md                | 4 ++--
 scripts/uboot-script-gen | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index fe5d2052cc69..3b4b16f1f7e4 100644
--- a/README.md
+++ b/README.md
@@ -80,8 +80,8 @@ Where:
   though.
 
 - BOOT_CMD specifies the u-boot command used to boot the binaries.
-  By default, it is 'booti'. The acceptable values are 'booti', 'bootm'
-  and 'bootefi' and 'none'. If the value is 'none', the BOOT_CMD is not
+  By default, it is 'booti'. The acceptable values are 'booti', 'bootm',
+  'bootz' and 'bootefi' and 'none'. If the value is 'none', the BOOT_CMD is not
   added to the boot script, and the addresses for the Xen binary and the
   DTB are stored in 'host_kernel_addr' and 'host_fdt_addr' u-boot
   env variables respectively, to be used manually when booting.
diff --git a/scripts/uboot-script-gen b/scripts/uboot-script-gen
index 6e52da5e2aca..9e3d86e4743a 100755
--- a/scripts/uboot-script-gen
+++ b/scripts/uboot-script-gen
@@ -1041,7 +1041,7 @@ function check_depends()
 
 function check_boot_cmd()
 {
-    if ! [[ " bootm booti bootefi none " =~ " ${BOOT_CMD}" ]]
+    if ! [[ " bootm booti bootz bootefi none " =~ " ${BOOT_CMD}" ]]
     then
         echo "\"BOOT_CMD=$BOOT_CMD\" is not valid"
         exit 1
-- 
2.25.1