EAP peer: Move certificate configuration params into shared struct

EAP peer: Move certificate configuration params into shared struct

These parameters for certificate authentication are identical for the
Phase 1 (EAP-TLS alone) and Phase 2 (EAP-TLS inside a TLS tunnel).
Furthermore, yet another copy would be needed to support separate
machine credential in Phase 2. Clean this up by moving the shared
parameters into a separate data struct that can then be used for each
need without having to define separate struct members for each use.

Signed-off-by: Jouni Malinen <j@w1.fi>