Move random-related defines to "crypto/rand.h"

Move random-related defines to "crypto/rand.h"

This fixes commit 01036e2afbe116d608be048ed15930fc885ab2a8, which moved the
DEVRANDOM and DEVRANDOM_EGD defines into rand_unix.c. That change introduced
the regression that the compiler complains about missing declarations in
crypto/info.c when OpenSSL is configured using `--with-rand-seed=devrandom`
(resp. `--with-rand-seed=egd`)

Fixes #10759

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10762)