mmc: ca_dw_mmc: add DesignWare based DM support for CAxxxx SoCs

Initial DesignWare based DM support for Cortina Access CAxxxx SoCs.

Signed-off-by: Arthur Li <arthur.li@cortina-access.com>
Signed-off-by: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>