ARM: integrator: merge platform.h to hardware.h

There is no need to have the two separate headers <mach/platform.h>
and <mach/hardware.h>, especially since we are now going to make them
local files. There is not one single driver outside the mach-integrator
folder referencing any of the files.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Jonathan Austin <jonathan.austin@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>