freescale: common: pfuze: define pfuze_mode_init only if defined(CONFIG_DM_PMIC)

pfuze_mode_init calls pmic_reg_read which is only available from

obj-$(CONFIG_$(SPL_TPL_)DM_PMIC) += pmic-uclass.o

Prepare for conversion of defined(CONFIG_DM_PMIC) to
CONFIG_IS_ENABLED(DM_PMIC).

Signed-off-by: Troy Kisky <troykiskyboundary@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>