clk: mvebu: share locks between gate clocks

Refactor mvebu_clk_gating_setup() to use a common spinlock instead of a
unique lock for every instance of a struct clk_gating_ctrl object. This
will be used later for a separate mux clock type that shares a register
with gate clock types and needs to use the same lock to protect access
to the register.

Cc: Andrew Lunn <andrew@lunn.ch>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

drivers/clk/mvebu/common.h

@@ -17,6 +17,8 @@
 
 #include <linux/kernel.h>
 
+extern spinlock_t ctrl_gating_lock;
+
 struct device_node;
 
 struct coreclk_ratio {