ARM: uniphier: change UNIPHIER_SERIAL to default y option

This is very likely to be necessary for normal use cases.
Set its default to 'y' for shorter defconfig files.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 9ff7234..ab5df70 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -344,6 +344,7 @@
 config UNIPHIER_SERIAL
 	bool "Support for UniPhier on-chip UART"
 	depends on ARCH_UNIPHIER
+	default y
 	help
 	  If you have a UniPhier based board and want to use the on-chip
 	  serial ports, say Y to this option. If unsure, say N.