MAINTAINERS: Add maintainers for Industry Pack subsystem

Add Samuel Iglesias Gonsalvez, Jens Taprogge and Greg Kroah-Hartman as
maintainers for the Industry Pack subsystem.

Cc: Jens Taprogge <jens.taprogge@taprogge.org>
Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>