bsd-user: Implement --seed and initialize random state

Copy --seed implementation (translated from linux-user's newer command
line scheme to the older one bsd-user still uses). Initialize the
randomness with the glib if a specific seed is specified or use the
qcrypto library if not.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>