README: update GitHub CI badges

The previous badge pointed to the `meta-ptx.yml` workflow file,
which is no longer used in any branch.
Instead the workflow now resides in `build.yml` in all branches.

Daily scheduled builds are triggered from `schedule-builds.yml` via
`workflow_dispatch` for all branches.
Display the status of the most recent `workflow_dispatch` build for all
currently supported branches.

Signed-off-by: Leonard Göhrs <[email protected]>

README.md

@@ -1,4 +1,6 @@
-[![meta-ptx CI](https://github.com/pengutronix/meta-ptx/workflows/meta-ptx%20CI/badge.svg)](https://github.com/pengutronix/meta-ptx/actions?query=workflow%3A%22meta-ptx+CI%22)
+| master | styhead | scarthgap | kirkstone |
+| ------ | ------- | --------- | --------- |
+| [![build (master)][gh_badge_master]][gh_action_master] | [![build (styhead)][gh_badge_styhead]][gh_action_styhead] | [![build (scarthgap)][gh_badge_scarthgap]][gh_action_scarthgap] | [![build (kirkstone)][gh_badge_kirkstone]][gh_action_kirkstone] |
 
 The meta-ptx layer provides support for classes and recipes that are meant to
 be public but did not make it into any other common layer, yet.
@@ -41,5 +43,14 @@ Maintainer: Enrico Jörns <[email protected]>
 
 Adding the ptx layer to your build
 ==================================
-
 Run ``bitbake-layers add-layer meta-ptx``.
+
+[gh_action_master]: https://github.com/pengutronix/meta-ptx/actions?query=event%3Aworkflow_dispatch+branch%3Amaster++
+[gh_action_styhead]: https://github.com/pengutronix/meta-ptx/actions?query=event%3Aworkflow_dispatch+branch%3Astyhead++
+[gh_action_scarthgap]: https://github.com/pengutronix/meta-ptx/actions?query=event%3Aworkflow_dispatch+branch%3Ascarthgap++
+[gh_action_kirkstone]: https://github.com/pengutronix/meta-ptx/actions?query=event%3Aworkflow_dispatch+branch%3Akirkstone++
+
+[gh_badge_master]: https://github.com/pengutronix/meta-ptx/actions/workflows/build.yml/badge.svg?branch=master&event=workflow_dispatch
+[gh_badge_styhead]: https://github.com/pengutronix/meta-ptx/actions/workflows/build.yml/badge.svg?branch=styhead&event=workflow_dispatch
+[gh_badge_scarthgap]: https://github.com/pengutronix/meta-ptx/actions/workflows/build.yml/badge.svg?branch=scarthgap&event=workflow_dispatch
+[gh_badge_kirkstone]: https://github.com/pengutronix/meta-ptx/actions/workflows/build.yml/badge.svg?branch=kirkstone&event=workflow_dispatch