ARM: dts: am335x-bone*: add DT for BeagleBone Black

The BeagleBone Black is basically a regular BeagleBone with eMMC and
HDMI added, so create a common dtsi both can use.

IMPORTANT: booting the existing am335x-bone.dts will blow up the HDMI
transceiver after a dozen boots with an uSD card inserted because LDO
will be at 3.3V instead of 1.8.

MMC support for AM335x still isn't in, so only the LDO change has been
added.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Tested-by: Tom Rini <trini@ti.com>
Tested-by: Matt Porter <matt.porter@linaro.org>
Acked-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>