BFQ: Change slice_idle to 0

As one can see in https://b.corp.google.com/issues/191606824,
slice_idle=0 works better for Android than slice_idle=8. Hence change
slice_idle from 8 to 0 for the second generation SoC.

See also
https://googleplex-android-review.git.corp.google.com/c/device/google/gs101/+/15415376.

Test: Untested
Change-Id: I2204047975b040a0255cf902132423d55710e131
Signed-off-by: Bart Van Assche <bvanassche@google.com>