am335x: Switch to CONFIG_SKIP_LOWLEVEL_INIT from guarding SPL or NOR_BOOT

In the case of SPL or NOR_BOOT (no SPL involved) we need to include
certain code in the build.  Use !CONFIG_SKIP_LOWLEVEL_INIT rather than
CONFIG_SPL_BUILD || CONFIG_NOR_BOOT to make the code clearer, and to
make supporting XIP QSPI boot clearer in the code.

Signed-off-by: Tom Rini <trini@ti.com>
Reviewed-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/ti/am335x/Makefile b/board/ti/am335x/Makefile
index c8b4f9a..804ac37 100644
--- a/board/ti/am335x/Makefile
+++ b/board/ti/am335x/Makefile
@@ -6,7 +6,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-ifeq ($(CONFIG_SPL_BUILD)$(CONFIG_NOR_BOOT),y)
+ifeq ($(CONFIG_SKIP_LOWLEVEL_INIT),)
 obj-y	:= mux.o
 endif
 
diff --git a/board/ti/am335x/board.c b/board/ti/am335x/board.c
index ce7a8b0..da780ed 100644
--- a/board/ti/am335x/board.c
+++ b/board/ti/am335x/board.c
@@ -82,7 +82,7 @@
 	return 0;
 }
 
-#if defined(CONFIG_SPL_BUILD) || defined(CONFIG_NOR_BOOT)
+#ifndef CONFIG_SKIP_LOWLEVEL_INIT
 static const struct ddr_data ddr2_data = {
 	.datardsratio0 = ((MT47H128M16RT25E_RD_DQS<<30) |
 			  (MT47H128M16RT25E_RD_DQS<<20) |