Attest: Configure token buffer in line with platform needs

Replace the hardcoded test token size with a use case dependent
constant provided by the Initial Attestation service interface
header file.
Store the test token buffer in the BSS segment instead of the
stack to prevent excessive stack usage on some platforms.

Change-Id: I8fa73ee3c79dbf2c425facad4f472979f42bd098
Signed-off-by: David Vincze <david.vincze@arm.com>
5 files changed