arm64: dts: ti: k3-am654-base-board: Add eMMC Support

On the am654x-evm, sdhci0 node is connected to an eMMC. Add node and
pinmux for the same.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>