modules: rename SOC_FAMILY_IMX

Rename SOC_FAMILY_IMX to SOC_FAMILY_NXP_IMX.

I've also kept SOC_FAMILY_IMX since there are
still legacy socs/boards that use it. When all
are ported to HWMv2 this should be removed.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>