mmc: dw_mmc-rockchip: add MMC_CAP_CMD23 capabilities

Add MMC_CAP_CMD23 for dw_mmc-rockchip, otherwise
failing to create rpmb partition. With it, we can
get rpmb successfully:

mmc1: new HS200 MMC card at address 0001
mmcblk0: mmc1:0001 DS2016 14.7 GiB
mmcblk0boot0: mmc1:0001 DS2016 partition 1 4.00 MiB
mmcblk0boot1: mmc1:0001 DS2016 partition 2 4.00 MiB
mmcblk0rpmb: mmc1:0001 DS2016 partition 3 4.00 MiB

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>