ARM: dts: Create bcm2708-rpi-b-rev1.dts

The first revision of the Pi Model B used I2C0 to address the camera
and I2C0 was available for user applications on the 26-pin header.
The second revision switched the roles, kept I2C0 on the 26-pin header
and added I2C1 on a new 8-way header (P5).

Up to now, downstream DTS has used a single file for both revisions of
the board, with a small amount of patching from the firmware. With the
introduction of an I2C mux to share I2C0 between the camera/display
connectors and the IDC headers, the difference between the two versions
becomes too great to comfortably manage with tweaking, hence this split.

Upstream DTS files already have bcm2835-rpi-b.dts and
bcm2835-rpi-b-rev2.dts, but for backwards compatibility the new file is
being added as bcm2708-rpi-b-rev1.dts, rather than renaming the old
shared version to bcm2708-rpi-b-rev2.dts.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>