I'd include contiki-conf.h in flash-cca.h and move this entire #if block there, leaving only the configuration value / platform default in contiki-conf.h

I know that I'm being a pain but do you think you can indent this with spaces and clean it up a little?
```
/* Backdoor enabled, on PA_3 (Select button) */
#define FLASH_CCA_BOOTLDR_CFG (FLASH_CCA_BOOTLDR_CFG_ENABLE \
  | ((3 << FLASH_CCA_BOOTLDR_CFG_PORT_A_PIN_S) & FLASH_CCA_BOOTLDR_CFG_PORT_A_PIN_M))
```
or something like that