Instead of relying on vendor.thermal.link_ready property to gate write
to BCL's SYSFS node, adding mitigation ready SYSFS so that writes to
BCL's SYSFS node would not cause NULL pointer dereference.
Bug: 249130916
Test: Confirm property vendor.brownout.mitigation.ready is set
Signed-off-by: George Lee <geolee@google.com>
Change-Id: Ic643a07ddb657cfc7e22537d5d25d0d99324e31c