hikey: Set alignment size 512B for fip building

Set alignment size to 512B so finally we can get fip.bin with 512B
alignment. This can avoid stuck issue for 'fastboot' downloading if
USB driver uses DMA for data transferring.
Signed-off-by: Leo Yan <leo.yan@linaro.org>

plat/hisilicon/hikey/platform.mk

@@ -119,3 +119,5 @@ endif
 ERRATA_A53_836870		:=	1
 ERRATA_A53_843419		:=	1
 ERRATA_A53_855873		:=	1
+
+FIP_ALIGN			:=	512