bcm2836 SoC support (used in Raspberry Pi 2 model B)

bcm2836 SoC support (used in Raspberry Pi 2 model B)

The bcm2835 and bcm2836 are essentially identical, except:
- The CPU is an ARM1176 v.s. a quad-core Cortex-A7.
- The physical address of many IO controllers has moved.

Rather than introducing a whole new bcm2836 value for $(SOC) or $(ARCH),
update the existing bcm2835 code to handle the minor differences, and
plumb it into the ARMv7 CPU architecture.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>