kernel: boot_delay: change to busy wait instaed of wait
kernel: boot_delay: change to busy wait instaed of wait

Intention of CONFIG_BOOT_DELAY is to delay booting of system for certain
time. Currently it is only delaying start of _main thread as delay is
created using k_sleep. This leads to putting _main thread into timeout
queue and continue kernel boot. This is causing some of undesirable
effects in some of test Automation usecase.
This patch changes k_sleep to k_busy_wait which result in delay in OS
boot instead of delaying start of _main.

Signed-off-by: Youvedeep Singh <7f33386d52951c3e7a699b9509267436d9be79f8@intel.com>
Signed-off-by: Anas Nashif <0d9952ec84ac43c159f6b7e7ed99a9080c00dd6e@intel.com>

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