asurada: implement board_set_charge_limit
asurada: implement board_set_charge_limit

BUG=b:160824663
TEST=`charger` command shows "I_in: 3000" on a usb-c charger.
BRANCH=master

Signed-off-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@google.com>
Change-Id: I5305560c3cdcf382bff017df2d14424ad3784e96
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2289492
Tested-by: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>
Reviewed-by: Eric Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@chromium.org>
Commit-Queue: Ting Shen <c671d3efec3d7e7e285f3788bf0d1ba4c8605b78@chromium.org>

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