feat(arch): Add AArch64 / ARMv8i CPU support, cross-compilation & Linux Kconfig TUI

- Implement AArch64 HAL, vector table (16 aligned vectors), GICv2, Generic Timer, Stage-1 MMU (39-bit VA), PL011 UART
- Build unified multi-architecture abstraction layer in include/arch/arch.h
- Create interactive Linux-like Kconfig TUI menuconfig in scripts/kconfig/menuconfig.py
- Support make menuconfig, defconfig, x86_64_defconfig, aarch64_defconfig
- Update master Makefile for cross-compiling x86_64 (x86_64-elf-) and AArch64 (aarch64-linux-gnu-)
- Dynamic architecture awareness across printk, uname, neofetch, and LazyBox

include/kernel/kernel.h

@@ -3,7 +3,7 @@
 
 #include "types.h"
 #include "printk.h"
-#include <arch/x86_64/io.h>
+#include <arch/arch.h>
 
 #define KERNEL_NAME        "SUB-OS"
 #define KERNEL_VERSION     "0.2.0-lts"

include/kernel/sync.h

@@ -16,7 +16,13 @@ static inline void spinlock_init(spinlock_t* lock) {
 
 static inline void spin_lock(spinlock_t* lock) {
     while (__atomic_test_and_set(&lock->lock, __ATOMIC_ACQUIRE)) {
+#if defined(__x86_64__)
         __asm__ volatile ("pause");
+#elif defined(__aarch64__)
+        __asm__ volatile ("yield");
+#else
+        __asm__ volatile ("");
+#endif
     }
 }