drm/bridge: Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)

The video processing pipeline on the second output on the GE B850v3:

  Host -> LVDS|--(STDP4028)--|DP -> DP|--(STDP2690)--|DP++ -> Video output

Each bridge has a dedicated flash containing firmware for supporting the
custom design. The result is that in this design neither the STDP4028
nor the STDP2690 behave as the stock bridges would. The compatible
strings include the suffix "-ge-b850v3-fw" to make it clear that the
driver is for the bridges with the firmware which is specific for the GE
B850v3.

The driver is powerless to control the video processing pipeline, as the
two bridges behaves as a single one. The driver is only needed for
telling the host about EDID / HPD, and for giving the host powers to ack
interrupts.

This driver adds one i2c_device for each bridge, but only one
drm_bridge. This design allows the creation of a functional connector
that is capable of reading EDID from the STDP2690 while handling
interrupts on the STDP4028.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Martyn Welch <martyn.welch@collabora.co.uk>
Cc: Martin Donnelly <martin.donnelly@ge.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Enric Balletbo <enric.balletbo@collabora.com>
Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/ad92919f2eaff2623a551aac94cf11ef948ff9ee.1488555615.git.peter.senna@collabora.com