meta-agl-bsp: fix up unmatched build

meta-agl-bsp: fix up unmatched build

Changes:
- Remove U-Boot patch and associated bbappend that were required
  to build with kirkstone, they are no longer required.
- Remove LAYERSERIES_COMPAT tweak that was being done to the
  meta-sifive layer as it is no longer required.

Bug-AGL: SPEC-5145

Change-Id: Id729fe08d8b5e962636bbfa2db9538c40afabda5
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/29907
ci-image-build: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account