Fix UEFI build on FreeBSD by not including system headers

CLA: trivial
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NBen Kaduk <kaduk@mit.edu>
Reviewed-by: NTomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/9149)

crypto/rand/rand_unix.c

@@ -21,7 +21,7 @@
 #if defined(__linux)
 # include <asm/unistd.h>
 #endif
-#if defined(__FreeBSD__)
+#if defined(__FreeBSD__) && !defined(OPENSSL_SYS_UEFI)
 # include <sys/types.h>
 # include <sys/sysctl.h>
 # include <sys/param.h>