reef: Enable Host command that limits external charger voltage/current
reef: Enable Host command that limits external charger voltage/current

This command will be used to perform power validation.

BUG=none
BRANCH=none
TEST=ectool extpwrlimit command can be used to set the max voltage/current
drawn from external charger.

Change-Id: Ic258954c1e3a714be7f648e77234dab594227ce0
Signed-off-by: Shamile Khan <0b4042e69ed1abbbdd05548f229cef643986e254@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/388843
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

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