Abstract acceleration sensor and add support for SC7A20 chip used in P8

[StarGate01]

This PR has been broken out of #1050, and depends on / includes #1128 .

• Abstract the acceleration sensor driver to inherit from the new AccelerationSensor base class
• Add driver for the SC7A20 chip, use FIFO buffer for smoothing, similar to BMA421: Use internal FIFO for smoothing #1145 .
• The CMake configuration has been extended to support driver selection via DRIVER_ACC

[StarGate01]

The simulator fails to build because the signature of the constructor Pinetime::System::SystemTask::SystemTask was changed, it now expects a Pinetime::Drivers::AccelerationSensor instead of Pinetime::Drivers::Bma421.

Should I open a PR in InfiniSim?

[Riksu9000]

Eventually it will need to be fixed in InfiniSim, however it might be a bit early to do it now.

The fifo changes that affect the PineTime should be one PR, so the other is focused only on the new driver and reviews will be easier.

[StarGate01]

Ok, I moved the FIFO changes for the BMA421 to #1145 .