Update Raspberry Pi (3/4) templates to match meta-raspberrypi configuration

Update Raspberry Pi (3/4) templates to match meta-raspberrypi configuration

Update the templates to use the updated flags and configuration present in
meta-raspberrypi.

The previous template did not properly pull-in the u-boot fragments for the RPI4.

v4: the MACHINE in the AGL template for the RPI4 is now
    'raspberrypi4-64' as in upstream.
    CI will get support-patches through releng-scripts.

Bug-AGL: SPEC-3368
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Change-Id: Ia2acb54516464d433c64adfc7ba832ccfdf899c3