arm: Fix VFP state corruption during signal delivery

D37419 corrupts VFP context store on signal delivery and D38696 corrupts PCB
because it performs a binary copy between structures with different layouts.
Revert the problematic parts of these commits to have signals delivery
working. Unfortunately, there are more problems with these revisions and
more fixes need to be developed.

Fixes: 6926e2699ae55080f860488895a2a9aa6e6d9b4d
Fixes: 4d2427f2c4451babe1bad600ae02c8a7c66031fe
MFC after: 4 weeks