clk: zynq: Add dummy clock enable function

A lot of Xilinx drivers are checking -ENOSYS which means that clock driver
doesn't have enable function. Remove this checking from drivers and create
dummy enable function as was done for clk_fixed_rate driver by
commit 6bf6d81c1112 ("clk: fixed_rate: add dummy enable() function").

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/drivers/clk/clk_zynq.c b/drivers/clk/clk_zynq.c
index bf32d83..1f71b7d 100644
--- a/drivers/clk/clk_zynq.c
+++ b/drivers/clk/clk_zynq.c
@@ -444,11 +444,21 @@
 }
 #endif
 
+static int dummy_enable(struct clk *clk)
+{
+	/*
+	 * Add implementation but by default all clocks are enabled
+	 * after power up which is only one supported case now.
+	 */
+	return 0;
+}
+
 static struct clk_ops zynq_clk_ops = {
 	.get_rate = zynq_clk_get_rate,
 #ifndef CONFIG_SPL_BUILD
 	.set_rate = zynq_clk_set_rate,
 #endif
+	.enable = dummy_enable,
 };
 
 static int zynq_clk_probe(struct udevice *dev)