regulator: core: have _regulator_get() accept get_type argument

Instead of separate "exclusive" and "allow_dummy" arguments, that formed 3
valid combinations (normal, exclusive and optional) and an invalid one,
let's accept explicit "get_type", like we did in devm-managed code.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>