sparc64: Add basic validations to {pud,pmd}_bad().

sparc64: Add basic validations to {pud,pmd}_bad().

[ Upstream commit 26cf432551d749e7d581db33529507a711c6eaab ]

Instead of returning false we should at least check the most basic
things, otherwise page table corruptions will be very difficult to
debug.

PMD and PTE tables are of size PAGE_SIZE, so none of the sub-PAGE_SIZE
bits should be set.

We also complement this with a check that the physical address the
pud/pmd points to is valid memory.

PowerPC was used as a guide while implementating this.

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