This work has been rebased on top of main now that #1500 has been merged: https://github.com/flihp/hubris/tree/no_more_rom. I've picked a few minor nits along the way that include mostly cosmetic stuff:

• adding a 'use drv_lpc55_flash::Flash` instead of spelling out the full type each time it's used in a few spots
• removing use of lib_lpc55_romapi::FLASH_PAGE_SIZE and replacing it with drv_lpc55_flash::BYTES_PER_FLASH_PAGE
• making lib_lpc55_romapi::FLASH_PAGE_SIZE private so others aren't tempted to use it instead of the equivalent from drv_lpc55_flash (it's still used by lib_lpc55_romapi internally)

I've also run this code through the identity manufacturing process and it works as expected.