CMake -- Remove deprecated call to FetchContent_Populate(pico_sdk)

[henrygab]

Seems to give a direct 1:1 replacement function.
This is just to track this for later PR.

CMake Warning (dev) at /usr/local/share/cmake-3.30/Modules/FetchContent.cmake:1953 (message):
  Calling FetchContent_Populate(pico_sdk) is deprecated, call
  FetchContent_MakeAvailable(pico_sdk) instead.  Policy CMP0169 can be set to
  OLD to allow FetchContent_Populate(pico_sdk) to be called directly for now,
  but the ability to call it with declared details will be removed completely
  in a future version.
Call Stack (most recent call first):
  cmake/pico_sdk_import.cmake:61 (FetchContent_Populate)
  CMakeLists.txt:49 (include)

[wyattearp]

This is the same core issue as #92 sadly, by getting the correct picotool path items set ahead of time this should resolve itself.