Merge tag 'pull-maintainer-updates-280224-1' of https://gitlab.com/stsquad/qemu into staging

Testing, gdbstub and plugin updates:

  - fix some test/tcg license headers to GPLv2+
  - bump up check-tcg timeout to 120s
  - avoid re-building VM images too often
  - update OpenBSD to 7.4
  - use GDBFeature to build gdbstub XML
  - unify plugin vcpu count under qemu_plugin_num_vcpus
  - avoid spurious idle/resume callbacks on new vCPUs
  - ensure nios2-linux-user processes async work
  - call vcpu_init plugin callback through async work
  - define plugin helpers when registers being read
  - add plugin API for reading register values
  - add support for register tracking to execlog
  - update plugin docs with assumptions
  - mention plugins can trigger tb_flush in mttcg design doc

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* tag 'pull-maintainer-updates-280224-1' of https://gitlab.com/stsquad/qemu: (29 commits)
  docs/devel: plugins can trigger a tb flush
  docs/devel: document some plugin assumptions
  docs/devel: lift example and plugin API sections up
  contrib/plugins: extend execlog to track register changes
  contrib/plugins: fix imatch
  tests/tcg: expand insn test case to exercise register API
  plugins: add an API to read registers
  plugins: create CPUPluginState and migrate plugin_mask
  gdbstub: expose api to find registers
  plugins: Use different helpers when reading registers
  cpu: call plugin init hook asynchronously
  linux-user: ensure nios2 processes queued work
  plugins: fix order of init/idle/resume callback
  plugins: add qemu_plugin_num_vcpus function
  plugins: remove previous n_vcpus functions from API
  gdbstub: Add members to identify registers to GDBFeature
  hw/core/cpu: Remove gdb_get_dynamic_xml member
  gdbstub: Infer number of core registers from XML
  gdbstub: Simplify XML lookup
  gdbstub: Change gdb_get_reg_cb and gdb_set_reg_cb
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>