raspberrypi: agl_raspberrypi4.inc: Unpin kernel version

raspberrypi: agl_raspberrypi4.inc: Unpin kernel version

Now that the failure in create-combined-dtb has been resolved (by
patching dtc), we can unpin the version of linux-raspberrypi and use the
5.4 kernel series.

Bug-AGL: SPEC-3702

Signed-off-by: Paul Barker <pbarker@konsulko.com>
Change-Id: I0da4eb7ccd17d816477d28864185278084abd9b4
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25840
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>