phy: rockchip-inno-usb3: add phy_cp_test function for u3phy

phy: rockchip-inno-usb3: add phy_cp_test function for u3phy

The Inno USB3 PHY disable the ability to toggle the CP test
pattern by default. But when do do USB3 compliance test, it
need to change the CP test pattern according to the requirement
of oscilloscope.

This patch add phy_cp_test function to enable the USB3 PHY
to detect the negative pulse which from the Aux Out of the
oscilloscope in SSRX+, and then the USB3 PHY can toggle the
CP test pattern while do USB3 compliance test.

Change-Id: Idbdf937a7a032dcedfd5f207b2d6d5961ed27b15
Signed-off-by: William Wu <wulf@rock-chips.com>