[exosphere] Rewrite crt0/init and ld script

Integrate 5.x SMC API changes, add 4.x specific setup, implement target firmware selection

Refactor 32-bit register definitions

Fix warmboot vs cpu_on check

Add most of warmboot_main

Finish writing warmboot _crt0_

Fix bugs required to successfully hand off to kernel

Use the boot critical section

Fix coldboot init, Exosphere makes it to PK2LDR in this commit.

Rewrite relocation stuff

Fix the set_memory_registers_enable_mmu call

Fix ttbl init pointer arith bug, other fixes

Implement flush_dcache_all_tzram_pa and invalidate_icache_all_inner_shareable_tzram_pa for the crt0s

Implement and use set_memory_registers_enable_mmu

Fix wrongly named register in __set_memory_registers, add prototype

Use provided __libc_init_array and __libc_fini_array, bugfixes

Skeleton smcCpuOff, fix building, fix smcConfigureCarveout

Rewrite the memory map-related code... ...

...other style fixes, etc.

Move source files to src/, add Makefile, fix all build and linkage errors, etc.