mfd: core: Don't use devres functions before device is added

The supply aliases for the MFD devices were being added using devres but
the device hasn't been added at this point and as such we can't use
devres.

The MFD already has a function that removes devices this patch uses the
non-devres versions of the supply alias functions and adds an unregister
in mfd_remove_devices_fn.

Reported-by: Carlo Caione <carlo@caione.org>
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>