powerpc/book3s64/radix: Make radix_mem_block_size 64bit

Similar to commit 89c140bb ("pseries: Fix 64 bit logical memory block panic")
make sure different variables tracking lmb_size are updated to be 64 bit.

Fixes: af9d00e9

 ("powerpc/mm/radix: Create separate mappings for hot-plugged memory")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201007114836.282468-4-aneesh.kumar@linux.ibm.com