hw/openrisc: page-align FDT address

hw/openrisc: page-align FDT address

The QEMU-provided FDT was only being recognized by the kernel when it
was used in conjunction with -initrd. Without it, the magic bytes
wouldn't be there and the kernel couldn't load it. This patch fixes the
issue by page aligning the provided FDT.

Cc: Stafford Horne <shorne@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>