board/raspberrypi: add support for the new pi4

This is based on the pi3 defconfig. There is currently no 64-bit support
since the upstream kernel does not build in this configuration.

Signed-off-by: Michael Cullen <michael@michaelcullen.name>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/raspberrypi/genimage-raspberrypi4.cfg

@@ -0,0 +1,30 @@
+image boot.vfat {
+  vfat {
+    files = {
+      "bcm2711-rpi-4-b.dtb",
+      "rpi-firmware/cmdline.txt",
+      "rpi-firmware/config.txt",
+      "rpi-firmware/fixup4.dat",
+      "rpi-firmware/start4.elf",
+      "rpi-firmware/overlays",
+      "zImage"
+    }
+  }
+  size = 32M
+}
+
+image sdcard.img {
+  hdimage {
+  }
+
+  partition boot {
+    partition-type = 0xC
+    bootable = "true"
+    image = "boot.vfat"
+  }
+
+  partition rootfs {
+    partition-type = 0x83
+    image = "rootfs.ext4"
+  }
+}