C++-ize W6300 driver: remove vtable indirection, constexpr pins, pragma once

CMakeLists.txt

@@ -11,11 +11,11 @@ pico_sdk_init()
 
 add_executable(picomap
 	picomap.cpp
-	w6300/wizchip_spi.c
-	w6300/wizchip_qspi_pio.c
-	w6300/wizchip_conf.c
-	w6300/w6300.c
-	w6300/socket.c
+	w6300/wizchip_spi.cpp
+	w6300/wizchip_qspi_pio.cpp
+	w6300/wizchip_conf.cpp
+	w6300/w6300.cpp
+	w6300/socket.cpp
 )
 
 target_include_directories(picomap PRIVATE