paritition_table: Verify the partition table md5sum when loading the app

Additionally, always enable the partition MD5 check if flash encryption is on in
Release mode. This ensures the partition table ciphertext has not been modified
(CVE-2021-27926).

The exception is pre-V3.1 ESP-IDF bootloaders and partition tables, which
don't have support for the MD5 entry.

components/bootloader_support/src/flash_partitions.c

@@ -52,7 +52,7 @@ esp_err_t esp_partition_table_verify(const esp_partition_info_t *partition_table
             MD5Update(&context, (unsigned char *) partition_table, num_parts * sizeof(esp_partition_info_t));
             MD5Final(digest, &context);
 
-            unsigned char *md5sum = ((unsigned char *) part) + 16; // skip the 2B magic number and the 14B fillup bytes
+            unsigned char *md5sum = ((unsigned char *) part) + ESP_PARTITION_MD5_OFFSET;
 
             if (memcmp(md5sum, digest, sizeof(digest)) != 0) {
                 if (log_errors) {