mx25pdk: Remove lowlevel_init.S file

As the lowlevel_init function is empty we should better
remove this assembly file entirely and use a dummy C
function instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/board/freescale/mx25pdk/mx25pdk.c b/board/freescale/mx25pdk/mx25pdk.c
index 01dac72..788d3c3 100644
--- a/board/freescale/mx25pdk/mx25pdk.c
+++ b/board/freescale/mx25pdk/mx25pdk.c
@@ -186,3 +186,6 @@
 
 	return 0;
 }
+
+/* Lowlevel init isn't used on mx25pdk, so just provide a dummy one here */
+void lowlevel_init(void) {}