DPE: Test: Refactor certificate chain creation based on test data

Simplify internal APIs and test code:
 - Extend test data definition to be able to save the valid
   context_handles per component.
 - Factor out the code which is responsible for building a
   certificate chain based on hard-coded test data
   to a new file: dpe_test_common.c
 - Define new APIs to get/update the valid context_handles in
   the test data: dpe_test_common.c
 - Refactor the test code to manage the context_handles with the
   new API instead of saving them in local variables/arrays.
 - Introduce dpe_test_data array to hold all the individual
   hard-coded test data. This reduces the usage of extern
   variables across the test code.

Change-Id: I78129d57e5cf4e5a9275feab350e70a773916115
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
11 files changed