mfd: Add parameter to disable ab8500 battery management

This patch makes it possible to disable battery management
via a module boot parameter. When 'ab8500-core.no_bm=1' then
ab8500_btemp, ab8500_chargalg, ab8500_charger and ab8500_fg will
not be probed. This boot parameter is used for scripted testing
of the system.

Signed-off-by: Rickard Andersson <rickard.andersson@stericsson.com>
Reviewed-by: Jonas Aberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>