powerpc/powernv: Create OPAL sglist helper functions and fix endian issues

We have two copies of code that creates an OPAL sg list. Consolidate
these into a common set of helpers and fix the endian issues.

Signed-off-by: Anton Blanchard <anton@samba.org>
powerpc/powernv: Fix little endian issues in OPAL dump code

Signed-off-by: Anton Blanchard <anton@samba.org>
Remove SG_LIST_VERSION
Add endian annotations for opal flash code.