Auto merge of #124404 - jonathanpallant:arm-target-changes-new, r=chrisnc

Arm bare-metal target doc changes

Updates the Arm bare-metal target docs:

* Detailed pages for all the Cortex-M targets, including details about setting target-cpu and target-features to suit specific Arm models
* More detail about the difference between `eabi` and `eabihf`
* Marks the Embedded Devices Working Group Cortex-M Team as the maintainer of the Cortex-M targets

Author: bors