MAINTAINERS: add Andrew and Baoquan as kexec maintainers

Add Andrew as kexec/kdump maintainer because he has been helping review
and merge ready kexec/kdump patches.

And I would like to nominate myself as kexec maintainer because I always
try to review generic kexec codes.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Baoquan He <[e-mail]>
Acked-by: Dave Young <[e-mail]>
Acked-by: Simon Horman <[e-mail]>
Cc: Eric Biederman <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

MAINTAINERS

···
 F:	scripts/Makefile.kcsan
 
 KDUMP
+M:	Andrew Morton <[e-mail]>
 M:	Baoquan He <[e-mail]>
 R:	Vivek Goyal <[e-mail]>
 R:	Dave Young <[e-mail]>
···
 F:	include/linux/kernfs.h
 
 KEXEC
+M:	Andrew Morton <[e-mail]>
+M:	Baoquan He <[e-mail]>
 L:	[e-mail]
 W:	http://kernel.org/pub/linux/utils/kernel/kexec/
 F:	include/linux/kexec.h