mmc: dt-bindings: Add resets/reset-names for Mediatek MMC bindings

Add description for resets/reset-names.

Cc: <stable@vger.kernel.org> # v5.4+
Fixes: 966580ad ("mmc: mediatek: add support for MT7622 SoC")
Signed-off-by: Wenbin Mei <wenbin.mei@mediatek.com>
Tested-by: Frank Wunderlich <frank-w@public-files.de>
Link: https://lore.kernel.org/r/20200814014346.6496-2-wenbin.mei@mediatek.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/mtk-sd.txt

@@ -50,6 +50,8 @@ Optional properties:
 		     error caused by stop clock(fifo full)
 		     Valid range = [0:0x7]. if not present, default value is 0.
 		     applied to compatible "mediatek,mt2701-mmc".
+- resets: Phandle and reset specifier pair to softreset line of MSDC IP.
+- reset-names: Should be "hrst".
 
 Examples:
 mmc0: mmc@11230000 {