ia64: disable CONFIG_PERFMON at least for now

Al noted that the semantics of the ia64 perfmon mmap() is really wrong,
and can cause serious VM problems.  Before we look at whether it needs
to be fixed, let's see if anybody even uses it, and mark it broken.  It
may be that we can just remove the code entirely.
Reported-by: Alexander Viro <viro@zeniv.linux.org.uk>
Acked-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Stephane Eranian <eranian@google.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/Kconfig

@@ -455,6 +455,7 @@ config IA64_MCA_RECOVERY
 
 config PERFMON
 	bool "Performance monitor support"
+	depends on BROKEN
 	help
 	  Selects whether support for the IA-64 performance monitor hardware
 	  is included in the kernel.  This makes some kernel data-structures a