[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/omap5912/debug.c b/platform/omap5912/debug.c
index cb3ea29..d190fa0 100644
--- a/platform/omap5912/debug.c
+++ b/platform/omap5912/debug.c
@@ -87,7 +87,7 @@
 	return read_uart_reg(port, UART_RHR);
 }
 
-void dputc(char c)
+void _dputc(char c)
 {
 	if (c == '\n')
 		uart_putc(0, '\r');
@@ -110,9 +110,9 @@
 	PANIC_UNIMPLEMENTED;
 }
 
-void debug_halt(void)
+void platform_halt(void)
 {
-	dprintf("HALT: spinning forever...\n");
+	dprintf(ALWAYS, "HALT: spinning forever...\n");
 	for(;;);
 }