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/mpc8308/Kconfig b/board/gdsys/mpc8308/Kconfig
index cad458a..222ab0d 100644
--- a/board/gdsys/mpc8308/Kconfig
+++ b/board/gdsys/mpc8308/Kconfig
@@ -4,6 +4,13 @@
 	  Use the 'osdw', 'osdp', and 'osdsize' legacy commands required by
 	  gdsys devices.
 
+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.
+
 config SYS_FPGA0_BASE
 	hex
 	default E0600000
@@ -40,6 +47,9 @@
 config GDSYS_LEGACY_OSD_CMDS
 	default y
 
+config GDSYS_LEGACY_DRIVERS
+	default y
+
 endif
 
 if TARGET_STRIDER
@@ -55,6 +65,10 @@
 
 config GDSYS_LEGACY_OSD_CMDS
 	default y
+
+config GDSYS_LEGACY_DRIVERS
+	default y
+
 endif
 
 config CMD_IOLOOP