sdcard: Use kernel8.img for 64bit kernel image name

This helps the firmware to identify the kernel as 64bit
image

Signed-off-by: Khem Raj <raj.khem@gmail.com>

classes/sdcard_image-rpi.bbclass

@@ -35,6 +35,7 @@ KERNEL_INITRAMFS ?= ""
 # Kernel image name
 SDIMG_KERNELIMAGE_raspberrypi  ?= "kernel.img"
 SDIMG_KERNELIMAGE_raspberrypi2 ?= "kernel7.img"
+SDIMG_KERNELIMAGE_raspberrypi3-64 ?= "kernel8.img"
 
 # Boot partition volume id
 BOOTDD_VOLUME_ID ?= "${MACHINE}"