regulator: Build sysfs entries with static attribute groups

Instead of calling device_create_file() manually after the device
registration, put all in attribute groups and filter the unwanted ones
via is_visible callback.  This not only simplifies the code but also
avoids the possible race between the device registration and sysfs
registration.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>