clk: stm32f7: add clock driver for stm32f7 family

add basic clock driver support for stm32f7 to enable clocks required by
the peripherals.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/stm32f746-disco_defconfig b/configs/stm32f746-disco_defconfig
index f638ca0..8fcab9d 100644
--- a/configs/stm32f746-disco_defconfig
+++ b/configs/stm32f746-disco_defconfig
@@ -39,3 +39,4 @@
 CONFIG_STM32_QSPI=y
 CONFIG_OF_LIBFDT_OVERLAY=y
 # CONFIG_EFI_LOADER is not set
+CONFIG_CLK=y