ARM: uniphier: make u-boot-with-spl.bin really available

Commit d085ecd6 ("ARM: uniphier: switch to raw U-Boot image")
claimed that u-boot-with-spl.bin would be useful in its commit log,
but it was not available because the commit missed to define
CONFIG_SPL_MAX_SIZE.  Without it, CONFIG_SPL_PAD_TO is not defined
either (see include/config_fallbacks.h).  So, the SPL image is not
padded correctly.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

include/configs/uniphier.h

@@ -279,5 +279,6 @@
 
 #define CONFIG_SPL_TARGET			"u-boot-with-spl.bin"
 #define CONFIG_SPL_MAX_FOOTPRINT		0x10000
+#define CONFIG_SPL_MAX_SIZE			0x10000
 
 #endif /* __CONFIG_UNIPHIER_COMMON_H__ */