p14s: Add common/{cpu,gpu}/amd to imports

[shymega]

Description of changes

This is my first upstream contribution (intend to contribute configs for
my NUC, GPD, and ClockworkPi devices). Essentially, this change
resolves #492, by adding the common/{cpu,gpu}/amd Nix fragments to the
imports list for the Thinkpad P14s.

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input

I have not been able to test these changes in my own configuration, but I have run the unit tests, which passed, save for the following tests, listed below:

The following 4 test(s) failed:
./tests/run.py '<nixos-hardware/raspberry-pi/4>'
./tests/run.py '<nixos-hardware/asus/zephyrus/ga402>'
./tests/run.py '<nixos-hardware/asus/zephyrus/ga401>'
./tests/run.py '<nixos-hardware/lenovo/legion/16irx8h>'```