updated minimum required cmake version to 3.16

[gullradriel]

Latest cmake versions are giving a warning on CMakeLists files that are using a required version under 3.5.

That PR is fixing the warning by requiring a minimum version of 3.16 anywhere it was checked. I choosed 3.16 as it's the one used in a lots of other open source projects, and it's not too recent.

As an example, we checked that Ubuntu latest stable is using at least version 3.22, and Ubuntu noble based build container is having version 3.28.3

'firmware' cmake warnings:

CMake Deprecation Warning at hackrf/firmware/CMakeLists.txt:23 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.
CMake Deprecation Warning at hackrf/firmware/blinky/CMakeLists.txt:22 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.
CMake Deprecation Warning at hackrf/firmware/hackrf_usb/CMakeLists.txt:21 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.

'host' cmake warnings:

CMake Deprecation Warning at CMakeLists.txt:3 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.
CMake Deprecation Warning at libhackrf/CMakeLists.txt:24 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.
CMake Deprecation Warning at hackrf-tools/CMakeLists.txt:24 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell CMake that the project does not need compatibility with older versions.