mmc: dw_mmc: k3: add MMC_CAP_CMD23

Enables RPMB support for the on-board eMMC of the HiKey board as well
as for eMMC modules connected to the microSD slot.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>