MIPS: mm: Add back define for PAGE_SHARED

There are still some drivers using PAGE_SHARED constant so put it back.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/pgtable.h

@@ -25,6 +25,8 @@
 struct mm_struct;
 struct vm_area_struct;
 
+#define PAGE_SHARED	vm_get_page_prot(VM_READ|VM_WRITE|VM_SHARED)
+
 #define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | __READABLE | __WRITEABLE | \
 				 _PAGE_GLOBAL | _page_cachable_default)
 #define PAGE_KERNEL_NC	__pgprot(_PAGE_PRESENT | __READABLE | __WRITEABLE | \