fix flash algo generation script

[zjli-2019]

1. generate #define instead of const uint32_t;
2. add the missing field algo_flags.

[mbrossard]

It's not clear to me what you are trying to fix. I don't see any targets using FLASH_START / FLASH_SIZE. flash_start and flash_size might be problematic, but macros are not the solutions. I would rather add the region size to sectors_info but this is a larger project.

Making the flags explicit would be cleaner.

[zjli-2019]

1. A possible use case of flash_start and flash_size:

   target_cfg_t target_device = {
       .sectors_info                   = sectors_info,
       .sector_info_length             = (sizeof(sectors_info))/(sizeof(sector_info_t)),
       .flash_regions[0].start         = flash_start,
       .flash_regions[0].end           = flash_start + flash_size,
       //...

2. flags is supposed to be edited manually later, which is not the best solution, but slightly better than none.