cactus: adjust the number of EC context to max number of PEs

According to [1] and in context of FF-A v1.0 a secure partition must
have either one EC (migratable UP) or a number of ECs equal to the
number of PEs (pinned MP). Adjust the cactus manifest execution-context
fields to maximum number of PEs.

[1] https://trustedfirmware-a.readthedocs.io/en/latest/components/
secure-partition-manager.html#platform-topology

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I79aec4b685c8774acb9b52dd6b05674cebc6ad2e
3 files changed