um: Use RWSEM_GENERIC_SPINLOCK on x86

Commit d12337 (rwsem: Remove redundant asmregparm annotation)
broke rwsem on UML.

As we cannot compile UML with -mregparm=3 and keeping asmregparm only
for UML is inadequate the easiest solution is using RWSEM_GENERIC_SPINLOCK.

Thanks to Thomas Gleixner for the idea.
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Tested-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net
Cc: <stable@kernel.org> # .39.x
Link: http://lkml.kernel.org/r/%3C1306183893-26655-1-git-send-email-richard%40nod.at%3ESigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/um/Kconfig.x86

@@ -29,10 +29,10 @@ config X86_64
 	def_bool 64BIT
 
 config RWSEM_XCHGADD_ALGORITHM
-	def_bool X86_XADD
+	def_bool X86_XADD && 64BIT
 
 config RWSEM_GENERIC_SPINLOCK
-	def_bool !X86_XADD
+	def_bool !RWSEM_XCHGADD_ALGORITHM
 
 config 3_LEVEL_PGTABLES
 	bool "Three-level pagetables (EXPERIMENTAL)" if !64BIT