ARM: UniPhier: add CONFIG_SPL_MAX_FOOTPRINT

The Boot ROM of UniPhier platform only loads 64KB image.  We should
always make sure that SPL memory footprint is less than that.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/configs/uniphier.h

@@ -296,4 +296,6 @@
 
 #define CONFIG_SYS_NAND_U_BOOT_OFFS		0x10000
 
+#define CONFIG_SPL_MAX_FOOTPRINT		0x10000
+
 #endif /* __CONFIG_UNIPHIER_COMMON_H__ */