Move entropy_poll.h to library

`entropy_poll.h` is not supposed to be used by application code and
is therefore being made internal.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/tests/suites/test_suite_entropy.function b/tests/suites/test_suite_entropy.function
index d9ea441..8869896 100644
--- a/tests/suites/test_suite_entropy.function
+++ b/tests/suites/test_suite_entropy.function
@@ -1,6 +1,6 @@
 /* BEGIN_HEADER */
 #include "mbedtls/entropy.h"
-#include "mbedtls/entropy_poll.h"
+#include "entropy_poll.h"
 #include "mbedtls/md.h"
 #include "string.h"
 
diff --git a/tests/suites/test_suite_psa_crypto_entropy.function b/tests/suites/test_suite_psa_crypto_entropy.function
index 8c1fdab..3019b7b 100644
--- a/tests/suites/test_suite_psa_crypto_entropy.function
+++ b/tests/suites/test_suite_psa_crypto_entropy.function
@@ -5,7 +5,7 @@
 #include <psa/crypto.h>
 
 #include "mbedtls/entropy.h"
-#include "mbedtls/entropy_poll.h"
+#include "entropy_poll.h"
 
 /* Calculating the minimum allowed entropy size in bytes */
 #define MBEDTLS_PSA_INJECT_ENTROPY_MIN_SIZE MAX(MBEDTLS_ENTROPY_MIN_PLATFORM, MBEDTLS_ENTROPY_BLOCK_SIZE)
diff --git a/tests/suites/test_suite_psa_crypto_init.function b/tests/suites/test_suite_psa_crypto_init.function
index 5fa29d7..d612548 100644
--- a/tests/suites/test_suite_psa_crypto_init.function
+++ b/tests/suites/test_suite_psa_crypto_init.function
@@ -5,7 +5,7 @@
 #include "psa_crypto_invasive.h"
 
 #include "mbedtls/entropy.h"
-#include "mbedtls/entropy_poll.h"
+#include "entropy_poll.h"
 
 #define ENTROPY_MIN_NV_SEED_SIZE                                        \
     MAX(MBEDTLS_ENTROPY_MIN_PLATFORM, MBEDTLS_ENTROPY_BLOCK_SIZE)