i.MX6: mx6qsabrelite: Add splash screen support

Adds support for HDMI, two LVDS panels and one RGB panel to
the SABRE-Lite board.

Displays supported:
         HDMI		- 1024 x 768 for maximum compatibility
         Hannstar-XGA   - 1024 x 768 LVDS (Freescale part number MCIMX-LVDS1)
         wsvga-lvds     - 1024 x 600 LVDS (Boundary p/n Nit6X_1024x600)
         wvga-rgb       - 800 x 480 RGB (Boundary p/n Nit6X_800x480)

Since the ipuv3_fb display driver currently supports only a single display,
this code auto-detects panel by probing the HDMI Phy for Hot Plug Detect
or the I2C touch controller of the LVDS and RGB displays in the priority
listed above.

Setting 'panel' environment variable to one of the names above will
override auto-detection.

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>