HDMI Force RGB Option to Fix dfsdfsdfs

(under construction)

With some TV products, there is a bug in their HDMI implementation that sometimes trigger the selection of the wrong colorspace in a magenta/green display.
Here is an option to enforce the colorspace to RGB for this cases.
Here are the more investigations and discussions in ODROID Forum.

• http://forum.odroid.com/viewtopic.php?f=144&t=21780&hilit=forcergb
• http://forum.odroid.com/viewtopic.php?f=144&t=20415&p=145208#p145208

2. monitor

# Enable | Disable HDMI CEC Control                 
setenv hdmi_cec  "0"            # Disabled                      
# setenv hdmi_cec  "1"          # Enabled                       
# setenv hdmi_cec  "2"          # Enabled but disable auto TV switching ON
                                                  
# Force HDMI to use RGB colorspace regardless of TV request
# setenv hdmi_forcergb "0"      # Disabled         
setenv hdmi_forcergb "1"        # Enabled          

if test "${hdmi_cec}" = "0"; then setenv hdmitx "hdmitx=cec0"; fi
if test "${hdmi_cec}" = "1"; then setenv hdmitx "hdmitx=cecf"; fi
if test "${hdmi_cec}" = "2"; then setenv hdmitx "hdmitx=cec7"; fi

if test "${hdmi_forcergb}" = "1"; then setenv hdmitx "${hdmitx},forcergb"; fi

#setenv bootargs "${rootopt} ${consoleopt} hdmimode=${hdmimode} ${hdmitx} vout=${vout_mode} ............"
setenv bootargs ${bootargs} ${hdmitx}