ARM: bcm2835: Split the DT for peripherals from the DT for the CPU

The set of peripherals remained constant across bcm2835 (Raspberry Pi
1) and bcm2836 (Raspberry Pi 2), but the CPU was swapped out.  Split
the files so that we can include just peripheral setup in 2836.

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