[PPC32] Add SysRq-G support to our KGDB stub.

From David Woodhouse <dwmw2@infradead.org>.

arch/ppc/kernel/ppc-stub.c

@@ -105,6 +105,8 @@
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/smp_lock.h>
+#include <linux/init.h>
+#include <linux/sysrq.h>
 
 #include <asm/cacheflush.h>
 #include <asm/system.h>
@@ -855,3 +857,23 @@ kgdb_output_string (const char* s, unsigned int count)
 	return 1;
 }
 #endif
+
+static void sysrq_handle_gdb(int key, struct pt_regs *pt_regs,
+			     struct tty_struct *tty)
+{
+	printk("Entering GDB stub\n");
+	breakpoint();
+}
+static struct sysrq_key_op sysrq_gdb_op = {
+        .handler        = sysrq_handle_gdb,
+        .help_msg       = "Gdb",
+        .action_msg     = "GDB",
+};
+
+static int gdb_register_sysrq(void)
+{
+	printk("Registering GDB sysrq handler\n");
+	register_sysrq_key('g', &sysrq_gdb_op);
+	return 0;
+}
+module_init(gdb_register_sysrq);