arc: cache: Change dcache_available signature
arc: cache: Change dcache_available signature

This function returns an essential boolean type, just changing the
signature to return a boolean type.

Signed-off-by: Flavio Ceolin <979b9165500b0741b9d0500e2efd74fc1547bff7@intel.com>

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