tests: Add mbedtls_test_ prefix to *hexify functions

Add mbedtls_test_ prefix to hexify() and unhexify()
test helper functions.

Command to change *.function files:
find . -name "*.function" -exec awk -i inplace \
    '{sub(/(un|)hexify\>/,"mbedtls_test_&")}1' {} \;

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index b57fe19..e493131 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -706,7 +706,7 @@
     TEST_ASSERT( mbedtls_ecp_group_load( &mbedtls_pk_ec( pub )->grp, grp_id ) == 0 );
     TEST_ASSERT( mbedtls_ecp_point_read_string( &mbedtls_pk_ec( pub )->Q, 16, QX_str, QY_str ) == 0 );
 
-    slen_check = unhexify( sig_check, sig_str );
+    slen_check = mbedtls_test_unhexify( sig_check, sig_str );
 
     md_info = mbedtls_md_info_from_type( md_alg );
     TEST_ASSERT( md_info != NULL );