Merge remote-tracking branch 'remotes/philmd-gitlab/tags/led-api-20201026' into staging

API to model LED.

CI jobs results:
. https://cirrus-ci.com/build/4879251751043072
. https://gitlab.com/philmd/qemu/-/pipelines/207661784
. https://travis-ci.org/github/philmd/qemu/builds/738958191
. https://app.shippable.com/github/philmd/qemu/runs/891/summary/console

# gpg: Signature made Mon 26 Oct 2020 22:03:59 GMT
# gpg:                using RSA key FAABE75E12917221DCFD6BB2E3E32C2CDEADC0DE
# gpg: Good signature from "Philippe Mathieu-Daudé (F4BUG) <f4bug@amsat.org>" [full]
# Primary key fingerprint: FAAB E75E 1291 7221 DCFD  6BB2 E3E3 2C2C DEAD C0DE

* remotes/philmd-gitlab/tags/led-api-20201026:
  hw/arm/tosa: Replace fprintf() calls by LED devices
  hw/misc/mps2-scc: Use the LED device
  hw/misc/mps2-fpgaio: Use the LED device
  hw/arm/aspeed: Add the 3 front LEDs drived by the PCA9552 #1
  hw/misc/led: Emit a trace event when LED intensity has changed
  hw/misc/led: Allow connecting from GPIO output
  hw/misc/led: Add a LED device

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