drivers: stm32_gpio: remove test on CFG_DRIVERS_GPIO

Remove test on CFG_DRIVERS_GPIO inside stm32_gpio.c C source file.
CFG_* dependencies are addressed in makefile file (e.g. plat-*/conf.mk),
not in the driver source file.

Fixes: 1001585 ("drivers: stm32_gpio: remove GPIO access specific API functions")
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

Author: etienne-lms

core/drivers/stm32_gpio.c

@@ -31,10 +31,6 @@
 #include <trace.h>
 #include <util.h>
 
-#ifndef CFG_DRIVERS_GPIO
-#error stm32_gpio driver expects CFG_DRIVERS_GPIO
-#endif
-
 #define GPIO_PIN_MAX		15
 
 #define GPIO_MODER_OFFSET	U(0x00)