memory: samsung: exynos5422-dmc: Adjust polling interval and uptreshold

In order to react faster and make better decisions under some workloads,
benchmarking the memory subsystem behavior, adjust the polling interval
and upthreshold value used by the simple_ondemand governor.

Reported-by: Willy Wolff <willy.mh.wolff.ml@gmail.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>