add another flash chip for hallowing m0 express

A small number of hallowing m0 express boards were manufactured
with an incorrect flash chip (2MB instead of 8MB).

If you have received one of these boards, contact support AT adafruit
DOT com for refund/replacement options.

However, there's no need to make these boards e-waste. At the cost of a
few bytes of flash, we can make them work with this simple update,
as tested by a user who received one of the incorrectly manufactured
units.

Author: jepler

ports/atmel-samd/boards/hallowing_m0_express/mpconfigboard.mk

@@ -7,7 +7,7 @@ CHIP_VARIANT = SAMD21G18A
 CHIP_FAMILY = samd21
 
 SPI_FLASH_FILESYSTEM = 1
-EXTERNAL_FLASH_DEVICES = "W25Q64JVxQ, GD25Q64C"
+EXTERNAL_FLASH_DEVICES = "W25Q64JVxQ, GD25Q64C, W25Q16JVxQ"
 LONGINT_IMPL = NONE
 
 # To keep the build small