Use the 5.3 kernel for the bionic raspi3 images.

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.525.37) UNRELEASED; urgency=medium
+
+  * Use the linux-raspi2-5.3 kernel flavour for the raspi3 images.  This kernel
+    is required for proper pi4 support. (LP: #1859478)
+
+ -- Łukasz 'sil2100' Zemczak <lukasz.zemczak@ubuntu.com>  Mon, 13 Jan 2020 15:33:20 +0100
+
 livecd-rootfs (2.525.36) bionic; urgency=medium
 
   * Preserve apt preferences created by any package we install (i.e.

live-build/auto/config

@@ -882,7 +882,7 @@ case $ARCH in
 				;;
 			raspi3)
 				COMPONENTS='main restricted universe multiverse'
-				KERNEL_FLAVOURS=raspi2
+				KERNEL_FLAVOURS=raspi2-5.3
 				add_package install linux-firmware-raspi2 u-boot-rpi flash-kernel u-boot-tools wpasupplicant
 				BINARY_REMOVE_LINUX=false
 				;;