powerpc: Record vma->phys_addr in ioremap()

The vmalloc code can track the physical address of a vma, when the
vma is used for ioremap, if set it is displayed in /proc/vmallocinfo.

Because get_vm_area_caller() doesn't know it's being called for
ioremap() it's up to the arch code to set the phys_addr. A bunch
of other arch's do this, I'm not sure why powerpc doesn't?

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>