MAINTAINERS: add board bindings list to OMAP2+ files

Add list of OMAP2+ boards to the corresponding section

CC: linux-omap@vger.kernel.org
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Message-ID: <20230515074512.66226-3-andreas@kemnade.info>
Signed-off-by: Tony Lindgren <tony@atomide.com>