Some modules (like eHCA) want to map all of kernel memory, for this to
work with a relocated kernel, we need to export kernstart_addr so
modules can use PHYSICAL_START and memstart_addr so they could use
MEMORY_START.  Note that the 32bit code already exports these symbols.
Signed-off-By: NSonny Rao <sonnyrao@us.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>