ARC: smp: Introduce smp hook @init_early_smp for Master core

This adds a platform agnostic early SMP init hook which is called on
Master core before calling setup_processor()

  setup_arch()
     smp_init_cpus()
         smp_ops.init_early_smp()
     ...
     setup_processor()

How this helps:
 - Used for one time init of certain SMP centric IP blocks, before
   calling setup_processor() which probes various bits of core,
   possibly including this block

 - Currently platforms need to call this IP block init from their
   init routines, which doesn't make sense as this is specific to ARC
   core and not platform and otherwise requires copy/paste in all
   (and hence a possible point of failure)

e.g. MCIP init is called from 2 platforms currently (axs10x and sim)
which will go away once we have this.

This change only adds the hooks but they are empty for now. Next commit
will populate them and remove the explicit init calls from platforms.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/smp.h

@@ -45,12 +45,16 @@ extern int smp_ipi_irq_setup(int cpu, int irq);
  * struct plat_smp_ops	- SMP callbacks provided by platform to ARC SMP
  *
  * @info:		SoC SMP specific info for /proc/cpuinfo etc
+ * @init_early_smp:	A SMP specific h/w block can init itself
+ * 			Could be common across platforms so not covered by
+ * 			mach_desc->init_early()
  * @cpu_kick:		For Master to kickstart a cpu (optionally at a PC)
  * @ipi_send:		To send IPI to a @cpu
  * @ips_clear:		To clear IPI received at @irq
  */
 struct plat_smp_ops {
 	const char 	*info;
+	void		(*init_early_smp)(void);
 	void		(*cpu_kick)(int cpu, unsigned long pc);
 	void		(*ipi_send)(int cpu);
 	void		(*ipi_clear)(int irq);

arch/arc/kernel/setup.c

@@ -411,8 +411,9 @@ void __init setup_arch(char **cmdline_p)
 	if (machine_desc->init_early)
 		machine_desc->init_early();
 
-	setup_processor();
 	smp_init_cpus();
+
+	setup_processor();
 	setup_arch_memory();
 
 	/* copy flat DT out of .init and then unflatten it */

arch/arc/kernel/smp.c

@@ -42,8 +42,13 @@ void __init smp_prepare_boot_cpu(void)
 }
 
 /*
- * Initialise the CPU possible map early - this describes the CPUs
+ * Called from setup_arch() before calling setup_processor()
+ *
+ * - Initialise the CPU possible map early - this describes the CPUs
  *   which may be present or become present in the system.
+ * - Call early smp init hook. This can initialize a specific multi-core
+ *   IP which is say common to several platforms (hence not part of
+ *   platform specific int_early() hook)
  */
 void __init smp_init_cpus(void)
 {
@@ -51,6 +56,9 @@ void __init smp_init_cpus(void)
 
 	for (i = 0; i < NR_CPUS; i++)
 		set_cpu_possible(i, true);
+
+	if (plat_smp_ops.init_early_smp)
+		plat_smp_ops.init_early_smp();
 }
 
 /* called from init ( ) =>  process 1 */