Fix STM32H7 dual core inheritance again

[multiplemonomials]

Summary of changes

Noticed that the website generator CI job was printing some warnings about overriding some attributes that didn't exist and then dying with a foreign key error. Oops!

Turns out that I kinda messed up in my attempt to refactor these STM32H7 targets. Not only were there some typos, which weren't caught by the testing I did but were caught by the website generator, but also the inheritance order is backwards from how I expected it: the first target in the list of parent targets gets the highest "priority" and can override the attributes from the other targets. Interestingly, this is actually documented in the code if you know where to look.

To fix this, I swapped the "inherits" order and made the CM4/CM7 targets not inherit from any other targets, which should fix the issue by making sure that they have priority to override stuff from the base MCU targets.

Impact of changes

• Fix some errors configuring and building for STM32H7 dual core targets

Migration actions required

Documentation

---

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---