lib: os: cbprintf: use TOOLCHAIN_HAS_C_GENERIC macro instead
lib: os: cbprintf: use TOOLCHAIN_HAS_C_GENERIC macro instead

Since toolchain.h supplies the macro TOOLCHAIN_HAS_C_GENERIC to
indicate if the compiler supports C Generic, there is no need to
do the long chain of macro arithmetic in cbprintf header file.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr