fs_enet: cleanup clock API use

make the Freescale ethernet driver get, prepare and enable the FEC clock
during probe(); disable and unprepare the clock upon remove(), put is
done by the devm approach; hold a reference to the clock over the period
of use.

clock lookup is non-fatal as not all platforms provide clock specs in
their device tree; failure to enable specified clocks is fatal.

Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/fs_enet_pd.h

@@ -16,6 +16,7 @@
 #ifndef FS_ENET_PD_H
 #define FS_ENET_PD_H
 
+#include <linux/clk.h>
 #include <linux/string.h>
 #include <linux/of_mdio.h>
 #include <linux/if_ether.h>
@@ -143,6 +144,8 @@ struct fs_platform_info {
 
 	int use_rmii;		/* use RMII mode 	       */
 	int has_phy;            /* if the network is phy container as well...*/
+
+	struct clk *clk_per;	/* 'per' clock for register access */
 };
 struct fs_mii_fec_platform_info {
 	u32 irq[32];