native_simulator: ensure nsi_host_random() returns 64 bits of randomness

[xudongzheng]

With native_sim/native/64, nsi_host_random() was only populating 31 of the 64 bits due to the 31-bit limit of the random() function.

To reproduce issue:

CONFIG_LOG=y
CONFIG_ENTROPY_GENERATOR=y
CONFIG_FAKE_ENTROPY_NATIVE_POSIX=y

#include <zephyr/logging/log.h>
#include <zephyr/random/random.h>

LOG_MODULE_REGISTER(hello);

int main(void) {
	uint8_t test[128];
	sys_csrand_get(test, sizeof(test));
	LOG_HEXDUMP_INF(test, sizeof(test), "test");
	return 0;
}

Output:

[00:00:00.000,000] <inf> hello: test
                                3b db 31 0f 00 00 00 00  cc b6 d5 47 00 00 00 00 |;.1..... ...G....
                                08 aa d2 15 00 00 00 00  e1 be 87 53 00 00 00 00 |........ ...S....
                                e4 7b 88 04 00 00 00 00  ae b1 9d 5f 00 00 00 00 |.{...... ..._....
                                e6 88 9e 4d 00 00 00 00  fb 2d 97 15 00 00 00 00 |...M.... .-......
                                50 16 f7 13 00 00 00 00  28 31 2f 70 00 00 00 00 |P....... (1/p....
                                c0 e6 44 39 00 00 00 00  e9 be 5f 25 00 00 00 00 |..D9.... .._%....
                                36 dc af 46 00 00 00 00  ef 48 d1 72 00 00 00 00 |6..F.... .H.r....
                                ed 48 03 3a 00 00 00 00  6d aa 0f 7e 00 00 00 00 |.H.:.... m..~....