git.cmake: git describe --always to support shallow clones
git.cmake: git describe --always to support shallow clones

There's no reason for BUILD_VERSION to work only when there are git
tags.

Signed-off-by: Marc Herbert <77e7c7d746b52c6eb01119b65a031ae1f650246d@intel.com>

finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr