kgdb, powerpc: arch specific powerpc kgdb support

This patch removes the old kgdb reminants from ARCH=powerpc and
implements the new style arch specific stub for the common kgdb core
interface.

It is possible to have xmon and kgdb in the same kernel, but you
cannot use both at the same time because there is only one set of
debug hooks.

The arch specific kgdb implementation saves the previous state of the
debug hooks and restores them if you unconfigure the kgdb I/O driver.
Kgdb should have no impact on a kernel that has no kgdb I/O driver
configured.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

arch/powerpc/platforms/powermac/setup.c

@@ -97,8 +97,6 @@ extern struct machdep_calls pmac_md;
 int sccdbg;
 #endif
 
-extern void zs_kgdb_hook(int tty_num);
-
 sys_ctrler_t sys_ctrler = SYS_CTRLER_UNKNOWN;
 EXPORT_SYMBOL(sys_ctrler);
 
@@ -329,10 +327,6 @@ static void __init pmac_setup_arch(void)
 	l2cr_init();
 #endif /* CONFIG_PPC32 */
 
-#ifdef CONFIG_KGDB
-	zs_kgdb_hook(0);
-#endif
-
 	find_via_cuda();
 	find_via_pmu();
 	smu_init();