x86_64: implement bootstrap function for pmap interface

arch/x86_64/pmap_ctrl.S

@@ -0,0 +1,31 @@
+
+	.global pmap_switch
+	.type pmap_switch, @function
+
+pmap_switch:
+	mov %rdi, %cr3
+	ret
+
+	.global gigabyte_pages
+	.type gigabyte_pages, @function
+
+gigabyte_pages:
+	push %rbp
+	mov %rsp, %rbp
+
+	push %rbx
+
+	mov $0x80000001, %eax
+	cpuid
+	andl $0x4000000, %edx
+
+	jz 2f
+
+1:	mov $0x1, %rax
+	jmp 3f
+
+2:	mov $0x0, %rax	
+
+3:	pop %rbx
+	pop %rbp
+	ret