arm64: fault: Print info about page table structure when dumping pte

Whilst debugging a remote crash, I noticed that show_pte is unhelpful
when it comes to describing the structure of the page table being walked.
This is easily fixed by printing out the page table (swapper vs user),
page size and virtual address size when displaying the PGD address.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>