[mlir] [integration-test] Let target check-mlir imply target check-mlir-integration too

Note that this does not mean that check-mlir will run check-mlir-integration
tests for all configurations. You still need to do a set up with the flag
MLIR_INCLUDE_INTEGRATION_TESTS set to ON in order to activate the integration test.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D82413