support MACHINE=raspberrypi3-64

The meta-raspberrypi layer already supports raspberrypi3-64, where
it will build a 64-bit kernel.

Add templates so that "aglsetup.sh -m raspberrypi3-64" works.

Note that 64-bit kernel build is only supported in the v4.9 branch of
the rpi kernel, and that the kernel image type is "Image" instead of Image.

Change-Id: Iee728191dc38521be607787d5736d21372f1dff5
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/9767
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>