ARM: integrator: read counter using syscon/regmap

Look up the core module base address from the device tree and
register a sched_clock() using the regmap to the core module
on the Integrator/CP.

MFD_SYSCON is selected by the arch so it is always available.

This further makes it possible to remove one more static map.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>