Fix Power testcase selection logic based on version

Some testcases vary depending on the version advertised by the platform;
when running with relaxed version checking (-r), checking the current
version with val_protocol_version_relaxed() returns true when the version
advertised by the platform is equal or greater than the expected one.

In this way you can run a test even against a newer SCMI server, which is
possibly still not fully supported by the ACS test-suite: full backward
compatibility cannot be assured, but you can run the testcases.

In order for all of this to work, relaxed protocol versions should be
checked starting from the latest/newest version supported.

When running without using relaxed checks, val_protocol_version_relaxed()
fallbacks to strict version-checking, so the ordering  of th checks is
unimportant.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>