kexec: generate VMCOREINFO for trace dump

kexec: generate VMCOREINFO for trace dump

The goal for this commit (and the next two) is to enable tools
to dump the trace buffer from /proc/vmcore at kdump time, without
requiring the kernel debug info package being installed.

makedumpfile processes VMCOREINFO section to dump dmesg buffer.
Extending VMCOREINFO to facilitate dumping trace buffer can be
very helpful in diagnosing system crash.

This is part one of three commits to generate symbol information
into VMCOREINFO section.

Orabug: 29770217
Signed-off-by: Isaac Chen <isaac.chen@oracle.com>
Reviewed-by: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>