armv8: fsl-layerscape: SPL size reduction

Compile-off mp.c and libfdt.c in case of SPL build. SPL size reduces
by approx 2k.

Signed-off-by: Sumit Garg <sumit.garg@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

arch/arm/cpu/armv8/fsl-layerscape/Makefile

@@ -7,8 +7,10 @@
 obj-y += cpu.o
 obj-y += lowlevel.o
 obj-y += soc.o
+ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_MP) += mp.o
 obj-$(CONFIG_OF_LIBFDT) += fdt.o
+endif
 obj-$(CONFIG_SPL) += spl.o
 obj-$(CONFIG_$(SPL_)FSL_LS_PPA) += ppa.o