Rename away from ROMBASEADDR

[reticulatedpines]

ROMBASEADDR is deceptive; it's not a base address, and it's definitely not the base address of the rom. This causes many people to locate their rom dumps at e.g. 0xe004_0000 on Digic 7 cams, when the actual base address is 0xe000_0000.

Currently we label the function at 0xe004_0000 as firmware_entry(). This is not terrible, but also a little deceptive, it's not truly an entry point. On Digic 7 cams the earliest code we know that runs is at 0xe000_0000, which jumps to bootloader like code, which if early checks succeed, jumps to firmware_entry(). We know 0xe004_0000 is the start of a block, it's packaged this way in FIR files.

Rename both of these to be less deceptive, and consistent. Proposal is firmware_start and dryos_start, as 0xe000_0000 and 0xe004_0000 respectively. This differs per cam model, 0xff0c_0000 on D45 would be dryos_start, 0xffff_0000 is firmware_start.

Refactor a bunch of stuff in code, but also docs and comments. Hopefully, ROMBASEADDR can be retired entirely, since we don't tend to care about where the rom itself is loaded.