define callback APIs for auxiliary firmware update.

TEST="COV=1 make" passes
	depthcharge still compiles
	in combination with follow-up CLs, ps8751 firmware update
	succeeds.

BUG=b:35586896

Change-Id: Ibadc41e56e4e25ee0aba5c83caa0e3596fb9ad20
Reviewed-on: https://chromium-review.googlesource.com/505259
Commit-Ready: Caveh Jalali <caveh@google.com>
Tested-by: Caveh Jalali <caveh@google.com>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
2 files changed