boot: remove framebuffer tag, fix bug

We will only work in raw character mode for now,
it's probably gonna take a *lot* of time until
we have an actual VGA driver qwq

boot/multiboot.S

@@ -56,6 +56,7 @@ entry_address_tag_start: /* struct mb2_header_tag_entry_address */
 	.long	_start
 entry_address_tag_end:
 
+#if 0 /* TODO: implement graphics */
 	.align	MB2_TAG_ALIGN
 framebuffer_tag_start: /* struct mb2_header_tag_framebuffer */
 	/* type */
@@ -71,6 +72,7 @@ framebuffer_tag_start: /* struct mb2_header_tag_framebuffer */
 	/* depth */
 	.long	32
 framebuffer_tag_end:
+#endif /* framebuffer disabled */
 
 	.align	MB2_TAG_ALIGN
 end_tag_start: /* struct mb2_header_tag */
@@ -87,7 +89,7 @@ header_end:
 	.text
 
 asmfn_begin(_start)
-	mov	_stack_end,	%esp
+	mov	$_stack_end,	%esp
 
 	/* reset EFLAGS */
 	pushl	$0