net: ks8851: fix link error

An object file cannot be built for both loadable module and built-in
use at the same time:

arm-linux-gnueabi-ld: drivers/net/ethernet/micrel/ks8851_common.o: in function `ks8851_probe_common':
ks8851_common.c:(.text+0xf80): undefined reference to `__this_module'

Change the ks8851_common code to be a standalone module instead,
and use Makefile logic to ensure this is built-in if at least one
of its two users is.

Fixes: 797047f8 ("net: ks8851: Implement Parallel bus operations")
Link: https://lore.kernel.org/netdev/20210125121937.3900988-1-arnd@kernel.org/Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/micrel/Makefile

@@ -4,8 +4,6 @@
 #
 
 obj-$(CONFIG_KS8842) += ks8842.o
-obj-$(CONFIG_KS8851) += ks8851.o
-ks8851-objs = ks8851_common.o ks8851_spi.o
-obj-$(CONFIG_KS8851_MLL) += ks8851_mll.o
-ks8851_mll-objs = ks8851_common.o ks8851_par.o
+obj-$(CONFIG_KS8851) += ks8851_common.o ks8851_spi.o
+obj-$(CONFIG_KS8851_MLL) += ks8851_common.o ks8851_par.o
 obj-$(CONFIG_KSZ884X_PCI) += ksz884x.o

drivers/net/ethernet/micrel/ks8851_common.c

@@ -1057,6 +1057,7 @@ int ks8851_suspend(struct device *dev)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_suspend);
 
 int ks8851_resume(struct device *dev)
 {
@@ -1070,6 +1071,7 @@ int ks8851_resume(struct device *dev)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_resume);
 #endif
 
 static int ks8851_register_mdiobus(struct ks8851_net *ks, struct device *dev)
@@ -1243,6 +1245,7 @@ int ks8851_probe_common(struct net_device *netdev, struct device *dev,
 err_reg_io:
 	return ret;
 }
+EXPORT_SYMBOL_GPL(ks8851_probe_common);
 
 int ks8851_remove_common(struct device *dev)
 {
@@ -1261,3 +1264,8 @@ int ks8851_remove_common(struct device *dev)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_remove_common);
+
+MODULE_DESCRIPTION("KS8851 Network driver");
+MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>");
+MODULE_LICENSE("GPL");