ARM: bcm2835: Add device tree for Raspberry Pi model B+

The model B and B+ differ in the GPIO lines for ACT and PWR leds, and the
I2S interface.

Signed-off-by: Matthias Klein <matthias.klein@linux.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>