vmcoreinfo: add the symbol "phys_base"

Fix the problem that makedumpfile sometimes fails on x86_64 machine.

This patch adds the symbol "phys_base" to a vmcoreinfo data.  The
vmcoreinfo data has the minimum debugging information only for dump
filtering.  makedumpfile (dump filtering command) gets it to distinguish
unnecessary pages, and makedumpfile creates a small dumpfile.

On x86_64 kernel which compiled with CONFIG_PHYSICAL_START=0x0 and
CONFIG_RELOCATABLE=y, makedumpfile fails like the following:

 # makedumpfile -d31 /proc/vmcore dumpfile
 The kernel version is not supported.
 The created dumpfile may be incomplete.
 _exclude_free_page: Can't get next online node.

 makedumpfile Failed.
 #

The cause is the lack of the symbol "phys_base" in a vmcoreinfo data.
If the symbol "phys_base" does not exist, makedumpfile considers an
x86_64 kernel as non relocatable.  As the result, makedumpfile
misunderstands the physical address where the kernel is loaded, and it
cannot translate a kernel virtual address to physical address correctly.

To fix this problem, this patch adds the symbol "phys_base" to a
vmcoreinfo data.

Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>