drivers: st: move i2c driver in its own folder

The driver could be used for other devices than PMIC.

Change-Id: I4569e7c0028e52e1ff2fe9d38f11de11e95d1897
Signed-off-by: Yann Gautier <yann.gautier@st.com>

drivers/st/pmic/stm32_i2c.c → drivers/st/i2c/stm32_i2c.c

 /*
- * Copyright (c) 2016-2018, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2016-2019, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */

plat/st/stm32mp1/platform.mk

@@ -51,7 +51,7 @@ PLAT_BL_COMMON_SOURCES	+=	${LIBFDT_SRCS}						\
 				drivers/st/clk/stm32mp1_clkfunc.c			\
 				drivers/st/ddr/stm32mp1_ddr_helpers.c			\
 				drivers/st/gpio/stm32_gpio.c				\
-				drivers/st/pmic/stm32_i2c.c				\
+				drivers/st/i2c/stm32_i2c.c				\
 				drivers/st/pmic/stm32mp1_pmic.c				\
 				drivers/st/pmic/stpmu1.c				\
 				drivers/st/reset/stm32mp1_reset.c			\