tests: Removed the hello tests from .testignore

tests: Removed the hello tests from .testignore

The "hello" tests that were previously ignored are all functioning
correctly, and are therefore being re-included in the test suite. The
MIPS and SPARC tests have been tagged a "long" as we do not compile
these ISAs are part of our "quick" tests.

Change-Id: I3aa079b81b938a12da6993213d158e53bc4ae514
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32914
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>