exo2: rename exosphere2 -> exosphere

fusee: switch to use exo2 instead of exo1

Switch atmosphere's build target to C++20. (#952) ...

* ams: update to build with gcc10/c++20

* remove mno-outline-atomics

* ams: take care of most TODO C++20s

* fusee/sept: update for gcc10

* whoosh, your code now uses pre-compiled headers

* make: dependency fixes

fusee/exo/sept: additional fixes

fusee-secondary: reboot to fusee-primary, instead of rcm

fusee-primary: reboot to self, instead of to RCM

Add defines for atmosphere git revision.

atmosphere: extract API version management to common folder

fusee: Complete re-write of the hardware initialization code: ...

- Updated code to match hekate's;
- Improved nxboot (now boots firmwares 2.x successfully);
- Temporarily disabled built-in boot system module support;
- Fixed multiple bugs.

fusee: SDMMC driver re-design: ...

- Based on hekate's, linux's and u-boot's source code;
- Full support for SD and MMC;
- Fixes multiple issues;
- Deployed first in fusee-primary.

fusee: Code cleanup and style fixes.

Revamp all the Makefiles (thanks @fincs @WinterMute) ...

... dependencies are now properly handled (e.g. header changes, etc.)

Rewrote crt0, init, and chainloading code ...

start.s, init.c, linker.ld and linker.specs are meant
to be re-used by user applications, should they remove the defines
from init.c and the .chainloader* sections from the linker script

fusee: sdmmc: use v3 compatibility mode for it's simpler DMA ...

we may want to change this at some point to get 64-bit addressing?

Change fusee folder naming