x86: use the new generic strnlen_user() function

This throws away the old x86-specific functions in favor of the generic
optimized version.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3220d44..d700811 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -94,6 +94,7 @@
 	select GENERIC_TIME_VSYSCALL if X86_64
 	select KTIME_SCALAR if X86_32
 	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 
 config INSTRUCTION_DECODER
 	def_bool (KPROBES || PERF_EVENTS || UPROBES)