ec: Mock out mkbp_send_event in kasa test.
ec: Mock out mkbp_send_event in kasa test.

Very rarely, the kasa test triggers 52 lines of coverage in
common/mkbp_event.c, with the entry point mkbp_send_event(). Add an
empty implementation of that function to prevent any code from calling
into common/mkbp_event.c.

BRANCH=None
BUG=b:230610934
TEST=Ran kasa test 50 times

Signed-off-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@google.com>
Change-Id: I5adee0b44ce65af6dc2abddb57b004af7388d12f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3610685
Commit-Queue: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>
Reviewed-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>
Commit-Queue: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>
Tested-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>
Auto-Submit: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>

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