tests: Add mbedtls_test_ prefix to hexcmp()

Add mbedtls_test_ prefix to hexcmp() test helper
function.

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

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index cd9346e..8e7f60d 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -679,7 +679,7 @@
     return( 0 );
 }
 
-int hexcmp( uint8_t * a, uint8_t * b, uint32_t a_len, uint32_t b_len )
+int mbedtls_test_hexcmp( uint8_t * a, uint8_t * b, uint32_t a_len, uint32_t b_len )
 {
     int ret = 0;
     uint32_t i = 0;