Finished basic task switching mechansim

PCB is local to a process's address space.
Context switches are written in assembly.
Moved x86 headers to include/x86

include/x86/msr.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+enum msr_id_t
+{
+    MSR_APIC_BASE = 0x1B
+};
+
+struct msr_apic_base_t
+{
+    uint64_t reserved_1 : 8;
+    uint64_t bsp : 1;
+    uint64_t reserved_2 : 1;
+    uint64_t x2apic_enable : 1;
+    uint64_t apic_global_enable : 1;
+    uint64_t apic_base : 52;
+};
+
+void read_msr(enum msr_id_t msr_addr, uint64_t *value);
+
+void write_msr(enum msr_id_t msr_addr, uint64_t *value);