clk: fix compilation errors for poplar platform

Move clk_release_all() prototype and definition inside
OF_CONTROL flag to avoid following compilation error for
poplar platform:

aarch64:  +   poplar
+drivers/usb/host/built-in.o: In function `ehci_usb_remove':
+drivers/usb/host/ehci-generic.c:159: undefined reference to `clk_release_all'
+drivers/usb/host/built-in.o: In function `ehci_usb_probe':
+drivers/usb/host/ehci-generic.c:133: undefined reference to `clk_release_all'
+make[1]: *** [u-boot] Error 139
+make: *** [sub-make] Error 2

Introduced by 4e542c4 clk: add clk_release_all()

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/include/clk.h b/include/clk.h
index a905a41..c5988f7 100644
--- a/include/clk.h
+++ b/include/clk.h
@@ -98,6 +98,21 @@
  * @return 0 if OK, or a negative error code.
  */
 int clk_get_by_name(struct udevice *dev, const char *name, struct clk *clk);
+
+/**
+ * clk_release_all() - Disable (turn off)/Free an array of previously
+ * requested clocks.
+ *
+ * For each clock contained in the clock array, this function will check if
+ * clock has been previously requested and then will disable and free it.
+ *
+ * @clk:	A clock struct array that was previously successfully
+ *		requested by clk_request/get_by_*().
+ * @count	Number of clock contained in the array
+ * @return zero on success, or -ve error code.
+ */
+int clk_release_all(struct clk *clk, int count);
+
 #else
 static inline int clk_get_by_index(struct udevice *dev, int index,
 				   struct clk *clk)
@@ -110,6 +125,12 @@
 {
 	return -ENOSYS;
 }
+
+static inline int clk_release_all(struct clk *clk, int count)
+{
+	return -ENOSYS;
+}
+
 #endif
 
 /**
@@ -174,20 +195,6 @@
  */
 int clk_disable(struct clk *clk);
 
-/**
- * clk_release_all() - Disable (turn off)/Free an array of previously
- * requested clocks.
- *
- * For each clock contained in the clock array, this function will check if
- * clock has been previously requested and then will disable and free it.
- *
- * @clk:	A clock struct array that was previously successfully
- *		requested by clk_request/get_by_*().
- * @count	Number of clock contained in the array
- * @return zero on success, or -ve error code.
- */
-int clk_release_all(struct clk *clk, int count);
-
 int soc_clk_dump(void);
 
 #endif