clocksource: add common of_clksrc_init() function

It is desirable to move all clocksource drivers to drivers/clocksource,
yet each requires its own initialization function. We'd rather not
pollute <linux/> with a header for each function. Instead, create a
single of_clksrc_init() function which will determine which clocksource
driver to initialize based on device tree.

Based on a similar patch for drivers/irqchip by Thomas Petazzoni.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

include/asm-generic/vmlinux.lds.h

@@ -149,6 +149,14 @@
 #define TRACE_SYSCALLS()
 #endif
 
+#ifdef CONFIG_CLKSRC_OF
+#define CLKSRC_OF_TABLES() . = ALIGN(8);				\
+			   VMLINUX_SYMBOL(__clksrc_of_table) = .;	\
+			   *(__clksrc_of_table)				\
+			   *(__clksrc_of_table_end)
+#else
+#define CLKSRC_OF_TABLES()
+#endif
 
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
@@ -493,6 +501,7 @@
 	DEV_DISCARD(init.rodata)					\
 	CPU_DISCARD(init.rodata)					\
 	MEM_DISCARD(init.rodata)					\
+	CLKSRC_OF_TABLES()						\
 	KERNEL_DTB()
 
 #define INIT_TEXT							\