message: updated layout file to use X and W
diff: /* Layout for the micro:bit v2 board, used by the examples in this repository. */
  MEMORY {
  - FLASH (rx) : ORIGIN = 0x00040000, LENGTH = 256K
  - RAM (rwx) : ORIGIN = 0x20004000, LENGTH = 112K
  + FLASH (X) : ORIGIN = 0x00040000, LENGTH = 256K
  + RAM (W) : ORIGIN = 0x20004000, LENGTH = 112K
  }
  -MPU_MIN_ALIGN = 8K;
  -
  TBF_HEADER_SIZE = 0x48;
  INCLUDE libtock_layout.ld
  