lrdp: iommu: check for invalid entries while page table parsing

Check for invalid entries, when extracting the pagetables from ramdump.

Change-Id: I35250c4c47af9046636dc135cda5f7a6f882cd69
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>

linux-ramdump-parser-v2/aarch64iommulib.py

@@ -284,6 +284,10 @@ def get_mapping_info(ramdump, pg_table, index):
 
 def fl_entry(ramdump, fl_pte, skip_fl):
     fl_pg_table_entry = ramdump.read_u64(fl_pte)
+
+    if fl_pg_table_entry is None:
+        return (0, 0)
+
     sl_pte = fl_pg_table_entry & FLSL_BASE_MASK
 
     if skip_fl == 1: