drm/msm: mdp4 lvds: continue if the panel is not connected

Two issues:

1> Intializing panel specific bits without actual panel presence.
2> Bailing out if the detect_panel() return -ENODEV.

With the existing code if detect_panel() returns an error code the
driver would bail out without doing anything, However it could continue
intializing hdmi related things. This patch adds two things.

1> moves the panel specific intialization only if the panel is detected
2> let the driver continue with hdmi intialization if detect_panel()
return -ENODEV.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>