powerpc: p1_p2_rdb_pc: Enable p1_p2_rdb_pc to boot from SD Card with SPL

Enable p1_p2_rdb_pc to start from eSDHC with SPL.

Signed-off-by: Ying Zhang <b40530@freescale.com>
diff --git a/board/freescale/p1_p2_rdb_pc/Makefile b/board/freescale/p1_p2_rdb_pc/Makefile
index f8d0b35..202b4a5 100644
--- a/board/freescale/p1_p2_rdb_pc/Makefile
+++ b/board/freescale/p1_p2_rdb_pc/Makefile
@@ -21,6 +21,9 @@
 COBJS-y	+= spl_minimal.o tlb.o law.o
 
 else
+ifdef CONFIG_SPL_BUILD
+COBJS-y += spl.o
+endif
 
 COBJS-y        += $(BOARD).o
 COBJS-y        += ddr.o