AM57xx evm Rev A3 with SR2.0 platform have incompatible changes for HDMI
GPIO requiring new dtb support. This implies we have to properly identify
the platform now as well. Hence provide a different board name for the
Rev A3 variations.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>