sparc32: vm_area_struct access for old Sun SPARCs.

upstream commit 961246b4ed8da3bcf4ee1eb9147f341013553e3c

Commit e4c6bfd2d79d063017ab19a18915f0bc759f32d9 ("mm: rearrange
vm_area_struct for fewer cache misses") changed the layout of the
vm_area_struct structure, it broke several SPARC32 assembly routines
which used numerical constants for accessing the vm_mm field.

This patch defines the VMA_VM_MM constant to replace the immediate values.

Signed-off-by: Olivier DANET <odanet@caramail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>