zmake: Generate branch coverage reports
zmake: Generate branch coverage reports

Sample branches during coverage runs and display branch coverage in
coverage reports.

BUG=none
TEST=zmake coverage build/zephyr/test/drivers
BRANCH=none

Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Change-Id: I7d48826f39d9a6021e8bb1fbd3e489016d5ce7f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3198113
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Reviewed-by: Yuval Peress <50dc11c009bd4d7e9d9d15a383c1743ce5ee82ef@google.com>

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