conf/machine/raspberrypi5.conf: Use "Image"

"zImage" not supported on arm64 so set KERNEL_IMAGETYPE_DIRECT to
"Image" for Raspberry Pi 5 and avoid the following errors:

| make: *** No rule to make target 'zImage'.  Stop.
| ERROR: oe_runmake failed

This work was sponsored by GOVCERT.LU.

Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>

conf/machine/raspberrypi5.conf

@@ -21,3 +21,6 @@ SDIMG_KERNELIMAGE ?= "kernel_2712.img"
 SERIAL_CONSOLES ?= "115200;ttyAMA10"
 
 VC4DTBO ?= "vc4-kms-v3d"
+
+# "zImage" not supported on arm64 and ".gz" images not supported by bootloader yet
+KERNEL_IMAGETYPE_DIRECT ?= "Image"