powerpc/mm: Define _PAGE_SOFT_DIRTY unconditionally

Conditional PTE bit definition is confusing and results in coding error.
Reviewed-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -37,11 +37,7 @@
 #define _RPAGE_RSV3		0x0400000000000000UL
 #define _RPAGE_RSV4		0x0200000000000000UL
 
-#ifdef CONFIG_MEM_SOFT_DIRTY
 #define _PAGE_SOFT_DIRTY	_RPAGE_SW3 /* software: software dirty tracking */
-#else
-#define _PAGE_SOFT_DIRTY	0x00000
-#endif
 #define _PAGE_SPECIAL		_RPAGE_SW2 /* software: special page */
 
 #define _PAGE_PTE		0x4000000000000000UL	/* distinguishes PTEs from pointers */