mfd: ab8500-debugfs: Add tests for ab8540 based platform initialisations

Signed-off-by: Alexandre Torgue <alexandre.torgue@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>
Reviewed-by: Mattias WALLIN <mattias.wallin@stericsson.com>
Tested-by: Maxime COQUELIN <maxime.coquelin@stericsson.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>