twl-regulator has a collection of feature flags, some defined
in twl-core.c and  one defined in i2c/twl.h.
This is confusing for anyone adding a new feature flag.

So collect them together and place them in twl.h immediately
after the structure in which they are initially set.
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>