ARM: bcm2835: dt: Add root properties for Raspberry Pi

This patch adds root compatible properties for the following boards:
- Raspberry Pi Model A
- Raspberry Pi Model A+
- Raspberry Pi Model B
- Raspberry Pi Model B (no P5)
- Raspberry Pi Model B rev2
- Raspberry Pi Model B+
- Raspberry Pi Compute Module

Reviewed-by: Stephen Warren <swarren@wwwdotorg.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>