doc: Update emsk board debug and flash section
doc: Update emsk board debug and flash section

Due to support updated from 2.2 to 2.3, a debug script is provided
for emsk, so developer can directly debug the zephyr application
using commands such as follows.
+ make BOARD=em_starterkit debug

Signed-off-by: Huaqi Fang <bec4dcdd00b836ab08fb892bf30af995140f52f5@synopsys.com>

aceofall/zephyr-iotos,holtmann/zephyr,zephyriot/zephyr,kraj/zephyr,rsalveti/zephyr,bigdinotech/zephyr,pklazy/zephyr,nashif/zephyr,bigdinotech/zephyr,punitvara/zephyr,sharronliu/zephyr,kraj/zephyr,bigdinotech/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,runchip/zephyr-cc3220,holtmann/zephyr,finikorg/zephyr,zephyriot/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,sharronliu/zephyr,bigdinotech/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,pklazy/zephyr,bigdinotech/zephyr,punitvara/zephyr,kraj/zephyr,aceofall/zephyr-iotos,galak/zephyr,fractalclone/zephyr-riscv,finikorg/zephyr,zephyrproject-rtos/zephyr,fbsder/zephyr,rsalveti/zephyr,sharronliu/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3220,galak/zephyr,rsalveti/zephyr,mbolivar/zephyr,explora26/zephyr,rsalveti/zephyr,aceofall/zephyr-iotos,nashif/zephyr,zephyriot/zephyr,punitvara/zephyr,nashif/zephyr,nashif/zephyr,fbsder/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,holtmann/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,zephyriot/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,fractalclone/zephyr-riscv,aceofall/zephyr-iotos,aceofall/zephyr-iotos,explora26/zephyr,ldts/zephyr,mbolivar/zephyr,explora26/zephyr,mbolivar/zephyr,finikorg/zephyr,nashif/zephyr,zephyriot/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,sharronliu/zephyr,pklazy/zephyr,GiulianoFranchetto/zephyr,fractalclone/zephyr-riscv,punitvara/zephyr,Vudentz/zephyr,finikorg/zephyr,kraj/zephyr,runchip/zephyr-cc3220,runchip/zephyr-cc3220,ldts/zephyr,kraj/zephyr,Vudentz/zephyr,Vudentz/zephyr,fbsder/zephyr,rsalveti/zephyr,mbolivar/zephyr,pklazy/zephyr,fractalclone/zephyr-riscv,GiulianoFranchetto/zephyr,sharronliu/zephyr,fbsder/zephyr,pklazy/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,fbsder/zephyr,holtmann/zephyr,ldts/zephyr,explora26/zephyr,fractalclone/zephyr-riscv