drm: bridge: dw-hdmi: Remove unused functions

Most of the hdmi_phy_test_*() functions are unused. Remove them.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Tested-by: Nickey Yang <nickey.yang@rock-chips.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303172007.26541-2-laurent.pinchart+renesas@ideasonboard.com