hw/loongarch: virt: pass random seed to fdt

hw/loongarch: 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 is the same procedure that's done in b91b6b5a2c ("hw/microblaze:
pass random seed to fdt"), e4b4f0b71c ("hw/riscv: virt: pass random seed
to fdt"), c6fe3e6b4c ("hw/openrisc: virt: pass random seed to fdt"),
67f7e426e5 ("hw/i386: pass RNG seed via setup_data entry"), c287941a4d
("hw/rx: pass random seed to fdt"), 5e19cc68fb ("hw/mips: boston: pass
random seed to fdt"), 6b23a67916 ("hw/nios2: virt: pass random seed to fdt")
c4b075318e ("hw/ppc: pass random seed to fdt"), and 5242876f37
("hw/arm/virt: dt: add rng-seed property").

These earlier commits later were amended to rerandomize the RNG seed on
snapshot load, but the LoongArch code somehow already does that, despite
not having this patch here, presumably due to some lucky copy and
pasting.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20240905153316.2038769-1-Jason@zx2c4.com>
Signed-off-by: Song Gao <gaosong@loongson.cn>