meta-agl-bsp: Kingfisher updates

meta-agl-bsp: Kingfisher updates

Updates to work with the new scarthgap-v5.9.4 branch in meta-rcar:
- Remove ti-bt bbappend and other references, as using ti-bt has been
  dropped by upstream.
- Remove si-tools and ti-bt-firmware bbappend tweaks that were to
  support usrmerge, as upstream seems to have incorporated them.
- Replace IMAGE_NAME and IMAGE_LINK_NAME redefinitions with use of
  the new IMAGE_MACHINE_SUFFIX variable which achieves the same
  result.

Bug-AGL: SPEC-5191

Change-Id: Ice07296a8560e07ce4b5705e6c2fa9f47896bfa0
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/30248
Tested-by: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account