build: Fix distclean for gen_idt
build: Fix distclean for gen_idt

This patch removes the gen_idt subdirectory from the clean target as
this directory is no longer in use due to recent changes to the way the
gen_idt is generated.

Signed-off-by: Andy Gross <4ba87047449f5700e8758e3b1af36e94376c2fff@linaro.org>

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