This commit reorganizes the BootInfo struct definition so it can be
shared for all architectures.
The existing free extern "C" boot info variables have been removed and
replaced with a global BootInfo struct, 'g_boot_info'.
On x86-64, the BootInfo is directly copied from the Prekernel-provided
struct.
On AArch64 and RISC-V, BootInfo is populated during pre_init.
This commit adds minimal support for compiler-instrumentation based
memory access sanitization.
Currently we only support detection of kmalloc redzone accesses, and
kmalloc use-after-free accesses.
Support for inline checks (for improved performance), and for stack
use-after-return and use-after-return detection is left for future PRs.
