genrest: Generate RST links in a less hacky way
genrest: Generate RST links in a less hacky way

Use the new Kconfiglib expression printing customization functionality
to get rid of the hacky expr_str() overriding.

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

GiulianoFranchetto/zephyr,explora26/zephyr,Vudentz/zephyr,ldts/zephyr,Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,kraj/zephyr,nashif/zephyr,kraj/zephyr,explora26/zephyr,nashif/zephyr,punitvara/zephyr,explora26/zephyr,explora26/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,kraj/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,Vudentz/zephyr,punitvara/zephyr,ldts/zephyr,punitvara/zephyr,galak/zephyr,nashif/zephyr