mmc: dw_mmc-rockchip: Fix runtime PM support for internal phase support

mmc: dw_mmc-rockchip: Fix runtime PM support for internal phase support

RK3576 is the first platform to introduce internal phase support, and
subsequent platforms are expected to adopt a similar design. In this
architecture, runtime suspend powers off the attached power domain, which
resets registers, including vendor-specific ones such as SDMMC_TIMING_CON0,
SDMMC_TIMING_CON1, and SDMMC_MISC_CON. These registers must be saved and
restored, a requirement that falls outside the scope of the dw_mmc core.

Fixes: 59903441f5e4 ("mmc: dw_mmc-rockchip: Add internal phase support")
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: Marco Schirrmeister <mschirrmeister@gmail.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>