hammer: Change PWM frequency to 10 kHz
hammer: Change PWM frequency to 10 kHz

backlight driver required frequency between 5-100 kHz, let's pick
10 kHz.

BRANCH=none
BUG=chrome-os-partner:63010
TEST=Backlight works, scope output shows correct frequency.

Change-Id: I8355ea87824f368a76236c97b9e4b7d40eca5612
Reviewed-on: https://chromium-review.googlesource.com/444484
Commit-Ready: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>
Tested-by: Toshak Singhal <fa3399d73221f8032839f11f2a09f40d50a5e6a7@google.com>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec