armv8: layerscape: Enabled I-cache for SPL boot

Enable I-cache for SPL boot to boost performance. Earlier MMU was
enabled only for LS2080A and has since been dropped by commit
f539c8a4a7 ("armv8: ls2080a: Drop early MMU for SPL build").

Signed-off-by: York Sun <york.sun@nxp.com>

arch/arm/cpu/armv8/fsl-layerscape/spl.c

@@ -52,6 +52,7 @@ void spl_board_init(void)
 
 void board_init_f(ulong dummy)
 {
+	icache_enable();
 	/* Clear global data */
 	memset((void *)gd, 0, sizeof(gd_t));
 	board_early_init_f();