ALSA: ASoC: Drop device registration from GTA01 lm4857 driver

Device registration should be handled at the machine level and not
in the driver code itself.  This patch removes the device registration
from the driver code in preparation for moving it to the machine
definition.

[Squashed down two parts to this patch for bisectability - there's also
a third part adding registration of the device to the out of tree GTA01
machine driver -- broonie]

Signed-off-by: Jonas Bonn <jonas.bonn@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>