[posix] add power calibration support (#8293)

The actual output power of the Thread device may be determined by both
the Thread radio chip and the FEM. Consider the output power error of
the Thread radio chip and the gain error of the FEM, the actual output
power is inconsistent with the expected output power.  To guarantee
that the actual output power is accurate and meet the regulatory
requirements, the output power should be calibrated in the factory if
the output power is not accurate.

This commit contains the following changes:

- Adds a power calibration implementation
- Adds a config file to configure the target power for different
  countries
- Adds a tool for the factory to persist the power calibration data

CMakeLists.txt

@@ -209,6 +209,7 @@ if(OT_PLATFORM STREQUAL "simulation")
 endif()
 
 add_subdirectory(tests)
+add_subdirectory(tools)
 
 add_custom_target(print-ot-config ALL
                   COMMAND ${CMAKE_COMMAND}