ARM: u300: push down syscon registers

Get rid of the <mach/syscon.h> header as a prerequisite for
multiplatform support. Do this by pushing the registers down
to their respective drivers and deleting the unused remainder.

Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>