spl: ti: Avoid preloader_console_init if !CONFIG_SPL_SERIAL_SUPPORT

If CONFIG_SPL_SERIAL_SUPPORT is disabled then the build fails because
serial_init is undefined. Guard preloader_console_init() appropriately
to fix this.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 61d3071..794dbd0 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -471,6 +471,7 @@
 	jump_to_image_no_args(&spl_image);
 }
 
+#ifdef CONFIG_SPL_SERIAL_SUPPORT
 /*
  * This requires UART clocks to be enabled.  In order for this to work the
  * caller must ensure that the gd pointer is valid.
@@ -491,6 +492,7 @@
 	spl_display_print();
 #endif
 }
+#endif
 
 /**
  * spl_relocate_stack_gd() - Relocate stack ready for board_init_r() execution