gdsys: Introduce GDSYS_LEGACY_DRIVERS

Future gdsys boards will switch from the legacy drivers in board/gdsys/common
to DM-based drivers.

Define a Kconfig option that disables the legacy drivers.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/board/gdsys/p1022/Kconfig b/board/gdsys/p1022/Kconfig
index 8514d08..f515427 100644
--- a/board/gdsys/p1022/Kconfig
+++ b/board/gdsys/p1022/Kconfig
@@ -1,3 +1,10 @@
+config GDSYS_LEGACY_DRIVERS
+	bool
+	help
+	  Enable the gdsys legacy drivers under board/gdsys/common. If this
+	  option is not set, all relevant DM drivers must be configured for the
+	  device in question.
+
 if TARGET_CONTROLCENTERD
 
 config SYS_BOARD
@@ -9,4 +16,7 @@
 config SYS_CONFIG_NAME
 	default "controlcenterd"
 
+config GDSYS_LEGACY_DRIVERS
+	default y
+
 endif