x86/mm/kaiser: re-enable vsyscalls

To avoid breaking the kernel ABI.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
[Hugh Dickins: Backported to 3.2:
 - Leave out the PVCLOCK_FIXMAP user mapping, which does not apply to
   this tree
 - For safety added vsyscall_pgprot, and a BUG_ON if _PAGE_USER
   outside of FIXMAP.]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc arch/x86/include/asm/vsyscall.h
Simple merge

diff --cc arch/x86/kernel/hpet.c
Simple merge

diff --cc arch/x86/kernel/vsyscall_64.c
Simple merge

diff --cc arch/x86/mm/kaiser.c
Simple merge