GitLab

This patch unites reverted #22987 and CTT fix 23279.

PEM/DER casting removed,  allowing mbedtls to manage
certificate conversion by itself. Credresource loads
certificates that could be either PEM or DER encoded
to a linked list instead of pushing them to a buffer.

Change-Id: I6dd0d957721d59feaf70f3dd421bf65d7c02ef1d
Signed-off-by: Oleksii Beketov <ol.beketov@samsung.com>