powerpc: Wire up /proc/vmallocinfo to our ioremap()

powerpc: Wire up /proc/vmallocinfo to our ioremap()

This adds the necessary bits and pieces to powerpc implementation of
ioremap to benefit from caller tracking in /proc/vmallocinfo, at least
for ioremap's done after mem init as the older ones aren't tracked.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>