tests: Big endian support in bitfield test
tests: Big endian support in bitfield test

The BIT_INDEX() macro assumed little-endian. This commit adds
big-endian support, conditioned on the preprocessor define
CONFIG_BIG_ENDIAN.

Signed-off-by: Martin Åberg <37424e7fbe3f8590d57db5ed6ae5b8866742b6be@gaisler.com>

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