mmc: Replace "enhanced_area_en" attribute by "partition_setting_completed"

Replace ext_csd "enhanced_area_en" attribute by
 "partition_setting_completed". It was used whether or
 not enhanced user area is defined and without checks of
 EXT_CSD_PARTITION_SETTING_COMPLETED bit.

Signed-off-by: Grégory Soutadé <gsoutade@neotion.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>