zephyr:tests: Enable PLATFORM_EC_BRINGUP code paths for coverage
zephyr:tests: Enable PLATFORM_EC_BRINGUP code paths for coverage

Create a drivers variant where PLATFORM_EC_BRINGUP is enabled to
cover bringup code paths

BUG=None
BRANCH=NONE
TEST=./twister -T zephyr/test

Signed-off-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>
Change-Id: I3e487f33c2bb43aa459387efffbd3a3f0a3bafe7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4033899
Code-Coverage: Zoss <345cf107e82c70959d46f59d98bddc98ce458aff@prod.google.com>
Reviewed-by: Tomasz Michalec <c064a6042954d4ba0805003dc021b76413ff1548@google.com>

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