ARM: bcm283x: merge BCM2835/BCM2836 directories into mach-bcm283x

BCM2835 (used on Raspberry Pi) and BCM2836 (used on Raspberry Pi 2)
are similar enough.  One of the biggest differences is the ARM
processor.  It is reasonable to collect the source files into a
single place, arch/arm/mach-bcm283x/.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>