hw/nios2: virt: pass random seed to fdt

hw/nios2: virt: pass random seed to fdt

If the FDT contains /chosen/rng-seed, then the Linux RNG will use it to
initialize early. Set this using the usual guest random number
generation function. This FDT node is part of the DT specification.

Cc: Chris Wulff <crwulff@gmail.com>
Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Message-Id: <20220719120113.118034-1-Jason@zx2c4.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>