raspberry: switch pico back to the boot2 for W25Q16

Presumably, switching it to generic hurt performance a bit.

I verified that the build-raspberry_pi_pico/boot2_padded_checksummed.S
built file has the same checksum as the old
bs2_default_padded_checksummed.S

Author: jepler

ports/raspberrypi/boards/raspberry_pi_pico/mpconfigboard.mk

@@ -9,3 +9,5 @@ CHIP_FAMILY = rp2
 INTERNAL_FLASH_FILESYSTEM = 1
 
 CIRCUITPY__EVE = 1
+
+BOOT2_S_UPPER = sdk/src/rp2_common/boot_stage2/boot2_w25q080.S