refactor(plat/nxp/lx216x): refine variable definition

This patch will make BL2_BASE to be hex valaue but
not a shell command.
Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
Change-Id: Iebb86a0b9bc8cab1676bd8e898cf4a1b6d16f472

plat/nxp/soc-lx2160a/soc.def

@@ -91,7 +91,7 @@ OCRAM_SIZE := 0x40000
 # Location of BL2 on OCRAM
 BL2_BASE_ADDR	:=	$(shell echo $$(( $(OCRAM_START_ADDR) + $(NXP_ROM_RSVD) + $(CSF_HDR_SZ) )))
 # Covert to HEX to be used by create_pbl.mk
-BL2_BASE	:=	$$(echo "obase=16; ${BL2_BASE_ADDR}" | bc)
+BL2_BASE	:=	$(shell echo "0x"$$(echo "obase=16; ${BL2_BASE_ADDR}" | bc))
 
 # BL2_HDR_LOC is at  (OCRAM_ADDR + NXP_ROM_RSVD)
 # This value BL2_HDR_LOC + CSF_HDR_SZ should not overalp with BL2_BASE