ARM: stm32: use clock setup function defined in clock.c

Use the clock setup function defined in clock.c instead of setting the
clock bits directly in the drivers.
Remove register definitions of RCC in rcc.h as these are already
defined in the struct in stm32.h

Signed-off-by: Michael Kurz <michi.kurz@gmail.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>