dt-bindings: PCI: dra7xx: Add bindings for unaligned access in host mode

Update device tree binding documentation of TI's dra7xx PCI controller
for enabling unaligned mem access as applicable not just in EP mode but
in host mode as well.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>