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/arch/x86_64/cpuid.h

@@ -25,9 +25,17 @@ typedef struct {
 } cpu_info_t;
 
 static inline void cpuid(uint32_t leaf, uint32_t* eax, uint32_t* ebx, uint32_t* ecx, uint32_t* edx) {
+#if defined(__x86_64__)
     __asm__ volatile("cpuid"
                      : "=a"(*eax), "=b"(*ebx), "=c"(*ecx), "=d"(*edx)
                      : "a"(leaf), "c"(0));
+#else
+    (void)leaf;
+    if (eax) *eax = 0;
+    if (ebx) *ebx = 0;
+    if (ecx) *ecx = 0;
+    if (edx) *edx = 0;
+#endif
 }
 
 void cpuid_detect(cpu_info_t* info);