beltino: set force_read_tach for beltino-class platforms

force_read_tach allows us to get more accurate fan values. Measuring
based upon PWM duty cycle is inaccurate, especially for low duty cycles
where the fan may actually not be spinning.

BUG=chrome-os-partner:24363
TEST=Manual on Monroe and Panther. Set 25% PWM duty cycle, verify
that mosys reports 0 RPM and the fan is not actually spinning. Set 100%
duty cycle, verify that mosys reports ~4.5 - 6K RPM, depending on
platform / fan.
BRANCH=None

Change-Id: I52f3fab142f9906c882a50bf26d498e9f17a1000
Reviewed-on: https://chromium-review.googlesource.com/180100
Tested-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Commit-Queue: Bowgo Tsai <bowgotsai@chromium.org>
1 file changed