tpm: fix reading of permanent flags

The offset of the permanent flags structure is in a different
place in the response compared to what the code is doing,
which gives us a completely useless result.

Fix by replacing hand-crafted code with generic parser
infrastructure.

Signed-off-by: André Draszik <adraszik@tycoint.com>
Acked-by: Simon Glass <sjg@chromium.org>