board: stm32f429-disco: switch to DM STM32 clock driver

Use available DM clk_stm32f.c driver instead of dedicated
mach-stm32/stm32f4/clock.c.

Migrate periph_clock defines from stm32_periph.h directly in
CLK driver. These periph_clock defines will be removed when STMMAC,
TIMER2 and SYSCFG drivers will support DM CLK.

Enable also CLK flag.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/mach-stm32/stm32f4/Makefile b/arch/arm/mach-stm32/stm32f4/Makefile
index 63db820..86c81bb 100644
--- a/arch/arm/mach-stm32/stm32f4/Makefile
+++ b/arch/arm/mach-stm32/stm32f4/Makefile
@@ -8,4 +8,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-y += clock.o timer.o
+obj-y += timer.o