regulator: make 88pm860x sharing one driver structure

Remove a lot of driver structures in 88pm860x driver. Make regulators share
one driver structure.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>