xtensa: Use generic config PREEMPT definition

So that it can handle the new CONFIG_PREEMPT_COUNT.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Zankel <chris@zankel.net>

arch/xtensa/Kconfig

@@ -80,18 +80,7 @@ config XTENSA_UNALIGNED_USER
 
 	  Say Y here to enable unaligned memory access in user space.
 
-config PREEMPT
-	bool "Preemptible Kernel"
-	help
-          This option reduces the latency of the kernel when reacting to
-          real-time or interactive events by allowing a low priority process to
-          be preempted even if it is in kernel mode executing a system call.
-          Unfortunately the kernel code has some race conditions if both
-          CONFIG_SMP and CONFIG_PREEMPT are enabled, so this option is
-          currently disabled if you are building an SMP kernel.
-
-          Say Y here if you are building a kernel for a desktop, embedded
-          or real-time system.  Say N if you are unsure.
+source "kernel/Kconfig.preempt"
 
 config MATH_EMULATION
 	bool "Math emulation"