samples: Migrate CONFIG_CPLUSPLUS to CONFIG_CPP

No longer available CONFIG_CPLUSPLUS.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

samples/spi_controller/prj.conf

@@ -1,4 +1,4 @@
-CONFIG_CPLUSPLUS=y
+CONFIG_CPP=y
 CONFIG_ARDUINO_API=y
 CONFIG_SPI=y
 CONFIG_LOG=y