vmcore: clean up read_vmcore()

vmcore: clean up read_vmcore()

Clean up read_vmcore().  Part for objects in vmcore_list can be written
uniformly to part for ELF headers.  By this change, duplicate and
complicated codes are removed, so it's more clear to see what's done
there.

Also, by this change, map_offset_to_paddr() is no longer used.  Remove it.

Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>