devicetree: phy: rockchip-emmc optional add vendor prefix

Update the documentation and add the vendor prefix to the optional
properties referred in vendor-prefixes.yaml.
Follow up with
commit 8b5c2b45 ("phy: rockchip: set pulldown for strobe line in dts")
commit a8cef928 ("phy: rockchip-emmc: output tap delay dt property")
Signed-off-by: Chris Ruehl <chris.ruehl@gtsys.com.hk>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201215014409.905-2-chris.ruehl@gtsys.com.hkSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/phy/rockchip-emmc-phy.txt

@@ -16,9 +16,9 @@ Optional properties:
  - drive-impedance-ohm: Specifies the drive impedance in Ohm.
                         Possible values are 33, 40, 50, 66 and 100.
                         If not set, the default value of 50 will be applied.
- - enable-strobe-pulldown: Enable internal pull-down for the strobe line.
-                           If not set, pull-down is not used.
- - output-tapdelay-select: Specifies the phyctrl_otapdlysec register.
+ - rockchip,enable-strobe-pulldown: Enable internal pull-down for the strobe
+                                    line.  If not set, pull-down is not used.
+ - rockchip,output-tapdelay-select: Specifies the phyctrl_otapdlysec register.
                                     If not set, the register defaults to 0x4.
                                     Maximum value 0xf.