drm/i915: Split 64bit hexadecimal addresses to make them easier to read

Broadwell introduces large address spaces, greater than 32bits in width.
These require that we then store and print 64bit values. If we were to
zero pad them out to 16 hexadecimal places, we have to carefully count
the leading zeroes - which is easy to make a mistake. Conversely, if we
do not zero pad out to 16, but keep it padding to 8 hexadecimal places,
it is very easy to miss an address that is actually larger than 4GiB. A
suggested compromise is to insert a space between the upper and lower
dwords of the address so that we can continue with our accustom 32bit
parser. (Alternatively, we could do the equivalent in our userspace
decoder.)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>