samples: spi: bitbang: Fix missing pass conditions

The sample did not have defined pass condition and was failing
due to a timeout. Add harness: consol and an explicit regex matching
the sample's output so it can pass on a hw. In addition, a requirement
for a gpio_loopback fixture was added to the sample.yaml.

fixes: #45229

Signed-off-by: Maciej Perkowski <Maciej.Perkowski@nordicsemi.no>