[IO] rework dprintf to take a debug level, defined in DEBUGLEVEL

printf at the moment just calls dprintf, but soon will become
a seperate I/O queue.
diff --git a/platform/integrator/debug.c b/platform/integrator/debug.c
index ab9f901..0a2e058 100644
--- a/platform/integrator/debug.c
+++ b/platform/integrator/debug.c
@@ -93,7 +93,7 @@
 	return -1;
 }
 
-void dputc(char c)
+void _dputc(char c)
 {
 	uart_putc(0, c);
 }
@@ -114,9 +114,9 @@
 	PANIC_UNIMPLEMENTED;
 }
 
-void debug_halt(void)
+void platform_halt(void)
 {
-	dprintf("HALT: spinning forever...\n");
+	dprintf(ALWAYS, "HALT: spinning forever...\n");
 	for(;;);
 }