tests/functional: move aarch64 GPU test into own file

tests/functional: move aarch64 GPU test into own file

I want to expand the number of tests to cover a wide range of
configurations. That starts with splitting off from the normal virt
test from which it doesn't really share much code. We can also reduce
the timeout of the original virt test now it is now longer burdened
with testing the GPU.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-2-alex.bennee@linaro.org>