init_task: Replace CONFIG_HAVE_GENERIC_INIT_TASK

Now that all archs except ia64 are converted, replace the config and
let the ia64 select CONFIG_ARCH_INIT_TASK

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20120503085035.867948914@linutronix.de

diff --git a/arch/Kconfig b/arch/Kconfig
index 2dd8fdd..597b132 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -148,7 +148,8 @@
 config GENERIC_SMP_IDLE_THREAD
        bool
 
-config HAVE_GENERIC_INIT_TASK
+# Select if arch init_task initializer is different to init/init_task.c
+config ARCH_INIT_TASK
        bool
 
 config HAVE_REGS_AND_STACK_ACCESS_API