tests: spi_loopback: log start/end of test at INF level
tests: spi_loopback: log start/end of test at INF level

This makes it easier to distinguish which lines come from which tests.

Signed-off-by: Marti Bolivar <9d90ac4c7bf6a305f6bfd81a23c7859bc883380e@linaro.org>

GiulianoFranchetto/zephyr,finikorg/zephyr,rsalveti/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,zephyriot/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,fbsder/zephyr,galak/zephyr,kraj/zephyr,Vudentz/zephyr,kraj/zephyr,explora26/zephyr,kraj/zephyr,fbsder/zephyr,explora26/zephyr,Vudentz/zephyr,mbolivar/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,ldts/zephyr,punitvara/zephyr,explora26/zephyr,Vudentz/zephyr,rsalveti/zephyr,galak/zephyr,kraj/zephyr,punitvara/zephyr,fbsder/zephyr,galak/zephyr,nashif/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,finikorg/zephyr,galak/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,rsalveti/zephyr,nashif/zephyr,zephyriot/zephyr,aceofall/zephyr-iotos,zephyrproject-rtos/zephyr,zephyriot/zephyr,Vudentz/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,fbsder/zephyr,mbolivar/zephyr,punitvara/zephyr,ldts/zephyr,explora26/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,nashif/zephyr,ldts/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,fbsder/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,runchip/zephyr-cc3220,GiulianoFranchetto/zephyr,rsalveti/zephyr,finikorg/zephyr,rsalveti/zephyr,runchip/zephyr-cc3220,zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,kraj/zephyr