printk: Add padding support to string format specifiers
printk: Add padding support to string format specifiers

The numeric format specifiers already have this support, but strings
didn't. This makes it possible to add padding after strings, using
format specifiers such as %-10s.

Signed-off-by: Johan Hedberg <628991c7b0a19c384f9b99c21ec330ce952bb838@intel.com>

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