arm/qemuarm64-secureboot: use 5.10 kernel

qemuarm64-secureboot is failing to boot with the 5.13 kernel.  Use the
5.10 kernel until this can be addressed.

Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/xen.yml

@@ -4,7 +4,7 @@ header:
     - meta-virtualization.yml
 
 local_conf_header:
-  meta-virt:
+  meta-virt: |
     DISTRO_FEATURES:append = " virtualization xen"
 
 target:

meta-arm/conf/machine/qemuarm64-secureboot.conf

@@ -19,3 +19,5 @@ IMAGE_FSTYPES += "wic wic.qcow2"
 WKS_FILE ?= "qemuarm64.wks"
 WKS_FILE_DEPENDS = "trusted-firmware-a"
 IMAGE_BOOT_FILES = "${KERNEL_IMAGETYPE}"
+
+PREFERRED_VERSION_linux-yocto ?= "5.10%"