All OPP PLL1 settings are computed during cold boot and saved in RAM.
During standby mode transitions, they are saved in the context and
restored when coming back to normal mode.
stm32_get_pll1_settings_from_context() is added to get easily them in BL2.
stm32_are_pll1_settings_valid_in_context() is used in BL32 and determines
if settings are already computed or not.

Change-Id: I8bfe925be4e9a0dd2cce8bf5486f54584d1d1716
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>