arm64: dts: ti: k3-j721e-beagleboneai64: Fix mailbox node status

arm64: dts: ti: k3-j721e-beagleboneai64: Fix mailbox node status

[ Upstream commit 155e7635ed1f3814d94d12556a3a0fed41d05b76 ]

Mailbox nodes are now disabled by default. The BeagleBoard AI64 DT
addition went in at around the same time and must have missed that
change so the mailboxes are not re-enabled. Do that here.

Fixes: fae14a1cb8dd ("arm64: dts: ti: Add k3-j721e-beagleboneai64")
Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20230515172137.474626-1-afd@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>