kernel: add some basic features

+ feat list:
+ * gdt/idt
+ * brokie pmm

kernel/src/arch/aarch64/cpu.c

@@ -1,7 +1,17 @@
+/*
+ *  The Soaplin Kernel
+ *  Copyright (C) 2025 The SILD Project
+ *
+ *  cpu.c - AArch64 CPU control implementation.
+ */
+
 #if defined (__aarch64__)
 
 #include <arch/cpu.h>
 
+void arch_init_stage1() {
+}
+
 void hcf() {
     for (;;) {
         asm ("wfi");