Added external mfr522 library and made it CMakeable.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "third_party/mfrc522"]
+	path = third_party/mfrc522_integration/mfrc522
+	url = https://github.com/libdriver/mfrc522.git

CMakeLists.txt

@@ -14,9 +14,12 @@ set(CMAKE_CXX_STANDARD 17)
 
 pico_sdk_init()
 
+add_subdirectory(third_party/mfrc522_integration)
+
 add_executable(${PROJECT} main.c)
 
 target_link_libraries(${PROJECT} pico_stdlib)
+target_link_libraries(${PROJECT} mfrc522)
 
 pico_add_extra_outputs(${PROJECT})
 pico_enable_stdio_usb(${PROJECT} 1)

third_party/mfrc522_integration/CMakeLists.txt

@@ -0,0 +1,4 @@
+set(SRC ${CMAKE_CURRENT_SOURCE_DIR}/mfrc522/src)
+
+add_library(mfrc522 STATIC ${SRC}/driver_mfrc522.c)
+target_include_directories(mfrc522 PUBLIC ${SRC})