dts: vt8500: Add SDHC node to DTS file for WM8650

Since WM8650 has the same 'WMT' SDHC controller as WM8505, and the driver
is already in the kernel, this node enables the controller support for
WM8650

Signed-off-by: Roman Volkov <rvolkov@v1ros.org>
Reviewed-by: Alexey Charkov <alchark@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>