Enable tests in Mbed OS environment

Update Makefiles and config.pl to adapt to directory structure used
in Mbed OS.
diff --git a/scripts/config.pl b/scripts/config.pl
index 287f1f1..edd4200 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -53,7 +53,28 @@
 use warnings;
 use strict;
 
-my $config_file = "include/mbedtls/config.h";
+my $config_file;
+my $include_dir;
+my $library_dir;
+my $mbedtls_config_file = $ENV{"MBEDTLS_CONFIG_FILE"};
+
+if ( ( -d "../library") || ( -d "./library") )  {
+    # library directory is present, we are using Mbed TLS namespace
+    $config_file = "include/mbedtls/config.h";
+    $include_dir = "include";
+    $library_dir = "library";
+} else {
+    # library directory is not present, we are using Mbed OS namespace
+    $config_file = "inc/mbedtls/config.h";
+    $include_dir = "inc";
+    $library_dir = "src";
+}
+
+if ( length $mbedtls_config_file ) {
+    $mbedtls_config_file = substr $mbedtls_config_file, 1, -1;
+    $config_file = $include_dir . "/" . $mbedtls_config_file;
+}
+
 my $usage = <<EOU;
 $0 [-f <file> | --file <file>] [-o | --force]
                    [set <symbol> <value> | unset <symbol> | get <symbol> |
@@ -205,7 +226,7 @@
     chdir '..' or die;
 
     # Confirm this is the project root directory and try again
-    if ( !(-d 'scripts' && -d 'include' && -d 'library' && -f $config_file) ) {
+    if ( !(-d 'scripts' && -d $include_dir && -d $library_dir && -f $config_file) ) {
         die "If no file specified, must be run from the project root or scripts directory.\n";
     }
 }