soc: amlogic: Add Meson Clock Measure driver

The Amlogic Meson SoCs embeds a clock measurer IP to measure the internal
clock paths frequencies.
The precision is determined by stepping into the duration until the counter
overflows.
The debugfs slows a pretty summary and each clock can be measured
individually aswell.

Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>