ARM: Fix Versatile&Integrator includes to behave in the same way as Realview

Realview doesn't include mach/platform.h in mach/hardware.h, so
make versatile behave in the same way.  Also, move the definition
of __io_address() into mach/hardware.h, just like Realview.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>