drivers: i3c: mcux: fix config_get to return last config set

mcux_i3c_configure() was saving values to a ctrl_config_hal
struct, but config_get() was not returning the values in
that struct. Remove that struct from the static data of
the driver and instead just have it on the stack. We init
that struct as needed just before calling the SDK API
I3C_MasterInit(). There's no reason to keep it around.
Change mcux_i3c_configure() to save a copy of the configuration
in the static data common.ctrl_config, which is what is
returned by config_get().

Signed-off-by: Mike J. Chen <mjchen@google.com>