power: pmic: mtk-pwrap: use pmic compatible to select child info

power: pmic: mtk-pwrap: use pmic compatible to select child info

Change the logic for selecting pmic_children_info to use the compatible
string from the devicetree instead of expecting the pwrap (part of the
MCU) to correspond to the separate PMIC chip.

In addition to being more correct, it also saves a few lines of code for
each MCU type that is added by dropping the enum and type field.

Reviewed-by: Julien Stephan <jstephan@baylibre.com>
Link: https://patch.msgid.link/20260409-mtk-pmic-fixes-v2-6-73e83aa6345b@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>