booke/powerpc: define wimge shift mask to fix compilation error

This fixes below compilation error on SOCs where CONFIG_PHYS_64BIT
is not defined:

 arch/powerpc/kvm/e500_mmu_host.c: In function 'kvmppc_e500_shadow_map':
| arch/powerpc/kvm/e500_mmu_host.c:631:20: error: 'PTE_WIMGE_SHIFT' undeclared (first use in this function)
|    wimg = (*ptep >> PTE_WIMGE_SHIFT) & MAS2_WIMGE_MASK;
|                     ^
| arch/powerpc/kvm/e500_mmu_host.c:631:20: note: each undeclared identifier is reported only once for each function it appears in
| make[1]: *** [arch/powerpc/kvm/e500_mmu_host.o] Error 1
Signed-off-by: NBharat Bhushan <Bharat.Bhushan@freescale.com>
Signed-off-by: NScott Wood <scottwood@freescale.com>

arch/powerpc/include/asm/pte-fsl-booke.h

@@ -37,5 +37,7 @@
 #define _PMD_PRESENT_MASK (PAGE_MASK)
 #define _PMD_BAD	(~PAGE_MASK)
 
+#define PTE_WIMGE_SHIFT (6)
+
 #endif /* __KERNEL__ */
 #endif /*  _ASM_POWERPC_PTE_FSL_BOOKE_H */