zephyr: add compatible assert.h header
zephyr: add compatible assert.h header

Add a compatible header for "builtin/assert.h" which uses Zephyr's
assertion system.

BUG=b:167590251
BRANCH=none
TEST=compile with follow-up CLs

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Id6ead8fd664dca8c391c72325fd98c6990e5fc13
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2427099
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

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