phy: rockchip-emmc: output tap delay dt property

Update the rockchip-emmc phy to set the otapdlysec register with
a dt property. This was mentioned from Brian Norris when he sent
the path to set the default value in the driver.
This patch add a dt property 'output-tapdelay-select' u32 and allow
to set the 0x0-0xf. If not set in dts, the old default 0x4 applies.

Tested with our customized rk3399 to tune the eMMC.

Signed-off-by: Chris Ruehl <chris.ruehl@gtsys.com.hk>
Link: https://lore.kernel.org/r/20201202082507.3536-2-chris.ruehl@gtsys.com.hk


Signed-off-by: Vinod Koul <vkoul@kernel.org>