regulator: twl: add twl6030 set_mode

Current set_mode logic does not support 6030. The logic for 4030 is
not reusable for 6030 as the mode setting for 6030 now uses the new
CFG_STATE register. We hence rename the old get_status as being
specific to 4030.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Saquib Herman <saquib@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@vega.(none)>