full support for overlay breakpoints for pokeplat

[joshua-smith-12]

• overlay auto, overlay list are now functional: displays the loaded overlays as they become loaded
• need to ensure only code-containing sections are marked as overlaid (pokeplat produces 2 sections for each overlay for some reason, idk why)
• not 100% clear if unloading overlays works, needs testing.
• overlay mapping addresses to lines/breakpoints is still broken, something in breakpoint.c is not mapped correctly. (e.g. a breakpoint in choose_starter_app.c triggers in ov4, but in reality NEITHER of these are loaded, ov77 is!) --- my suspicion for this is the part of breakpoint.c that checks whether the correct overlay is loaded does not work right for these overlays, maybe it still checks VMA/LMA/etc.

[joshua-smith-12]

pokeplat produces 2 sections for each overlay for some reason, idk why - this might just be a quirk of the debuginfo, i think it's generating a pointer to the end of the section.

this can probably just be avoided by loading the 1st matching section only.

[joshua-smith-12]

^ https://github.com/joshua-smith-12/binutils-gdb-nds/commit/b8687aa568bc078511bd19a677398b71e6875a74

[joshua-smith-12]

all of the issues originally outlined are resolved. stepping still does not work.

[joshua-smith-12]

stepping works fine now, i think there was an issue with section mappings. i'll close this now. see branch nds-overlays