If a custom bl1 is used on sdcard, then it should be embedded at 0x200 (512). If a GPT filesystem is used, then the GPT header uses roughly the first 0x500 bytes, and hence bl1 overwrites part of the GPT header in that configuration. Change to msdos partition type so that the filesystem works fine whether or not we use stock bl1 or custom one. Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6442