Depending on the application, board code might want to configure
different power levels and brownout thresholds. They can do so now with
an additional struct mxs_power_ctrls* parameter to mx2*_power_init.

Note that VDDMEM was not set up explicitely in mx28_power_init, but can
now be configured. However, mx28_power_default->vddmem is NULL, so the
old behaviour is still the case when using those default values.

Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>