[flang][openacc] Apply mutually exclusive clauses restriction to routine (#77802)

this patch enforce or fix the enforcement of two restrictions from
section 2.15.1:

> Only the gang, worker, vector, seq and bind clauses may follow a
device_type clause.

`seq` was not allowed after `device_type` with the current
implementation.

> Exactly one of the gang, worker, vector, or seq clauses must appear.

This was not properly checked. This patch check correctly for mutually
exclusion as described in section 2.4. Mutually exclusive clauses may
appear on the same directive if they apply for different device_type.