net: dsa: lantiq_gswip: split into common and MMIO parts

Move all parts specific for the MMIO/SoC driver into a module of its own
to prepare for supporting MDIO-connected switch ICs.
Modify gswip_probe() functions by splitting it into a common function
gswip_probe_common() which covers allocating, initializing and registering
the DSA switch, while keeping transport-specific regmap initialization as
well as PHY firmware loading in the new MMIO/SoC-specific gswip_probe()
function.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/dc7da5b65ec220ba8e9bc4bd04fe1ed7de046656.1762170107.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/lantiq/Kconfig

@@ -1,8 +1,12 @@
+config NET_DSA_LANTIQ_COMMON
+	tristate
+	select REGMAP
+
 config NET_DSA_LANTIQ_GSWIP
 	tristate "Lantiq / Intel GSWIP"
 	depends on HAS_IOMEM
 	select NET_DSA_TAG_GSWIP
-	select REGMAP
+	select NET_DSA_LANTIQ_COMMON
 	help
 	  This enables support for the Lantiq / Intel GSWIP 2.1 found in
 	  the xrx200 / VR9 SoC.

drivers/net/dsa/lantiq/Makefile

@@ -1 +1,2 @@
 obj-$(CONFIG_NET_DSA_LANTIQ_GSWIP) += lantiq_gswip.o
+obj-$(CONFIG_NET_DSA_LANTIQ_COMMON) += lantiq_gswip_common.o

drivers/net/dsa/lantiq/lantiq_gswip.h

@@ -278,4 +278,8 @@ struct gswip_priv {
 	u16 version;
 };
 
+void gswip_disable_switch(struct gswip_priv *priv);
+
+int gswip_probe_common(struct gswip_priv *priv, u32 version);
+
 #endif /* __LANTIQ_GSWIP_H */