Only install oem-20.04 kernel flavour on amd64, as it doesn't exist on other arches.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.654) UNRELEASED; urgency=medium
+
+  * Only install oem-20.04 kernel flavour on amd64, as it doesn't exist on
+    other arches.
+
+ -- Dimitri John Ledkov <xnox@ubuntu.com>  Fri, 13 Mar 2020 20:17:46 +0000
+
 livecd-rootfs (2.653) focal; urgency=medium
 
   * Stop trying to extract autoinstall config during boot, subiquity will do

live-build/auto/config

@@ -581,10 +581,15 @@ case $PROJECT in
 				LIVE_TASK='ubuntu-live'
 				add_task install minimal standard ubuntu-desktop
 				add_task live ubuntu-desktop-minimal-default-languages ubuntu-desktop-default-languages
+				KERNEL_FLAVOURS='generic'
+				case $ARCH in
+					amd64)
 						KERNEL_FLAVOURS='generic oem-20.04'
 						;;
 				esac
 				;;
+		esac
+		;;
 
 	kubuntu|kubuntu-dvd)
 		add_task install minimal standard