ARM: bcm2835: Add devicetree for bcm2836 and Raspberry Pi 2 B

The Pi 2 B ends up like a Pi 1 B+, with the same peripherals and
pinout, but the CPU and memory layout changed to use the 2836.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>