nand: mxc: Switch NAND SPL to generic SPL

This also fixes support for mx31pdk and tx25, which had been broken by commit
e05e5de7fae5bec79617e113916dac6631251156.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/board/karo/tx25/Makefile b/board/karo/tx25/Makefile
index 9617fa5..c26bf36 100644
--- a/board/karo/tx25/Makefile
+++ b/board/karo/tx25/Makefile
@@ -25,8 +25,10 @@
 
 LIB	= $(obj)lib$(BOARD).o
 
-COBJS	:= tx25.o
+ifdef CONFIG_SPL_BUILD
 SOBJS	:= lowlevel_init.o
+endif
+COBJS	:= tx25.o
 
 SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS))