pl010: Convert CONFIG_PL010_SERIAL to Kconfig

We want to use Kconfig logic to depend on whether pl01x devices
are built in, so let's convert their inclusion selection to Kconfig.

This round goes to pl010.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0b9eb11..f159124 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -348,6 +348,7 @@
 config TARGET_EDB93XX
 	bool "Support edb93xx"
 	select CPU_ARM920T
+	select PL010_SERIAL
 
 config TARGET_ASPENITE
 	bool "Support aspenite"