MAINTAINERS: add files related to kdump

Kdump is implemented based on kexec, however some files are only related
to crash dumping and missing, add them to KDUMP entry.

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Dave Young <dyoung@redhat.com>
Link: http://lkml.kernel.org/r/20200520103633.GW5029@MiWiFi-R3L-srv


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>