fix(stm32mp1_clk): keep RTC clock always on
fix(stm32mp1_clk): keep RTC clock always on

On battery powered systems the RTC keeps the date/time across
system reboot.
The RTC clock should not be disabled otherwise the date/time
counter gets stopped.

Tag RTC clock as always on.

Signed-off-by: HE Shushan <a43a89ea26fd362fd93f8378d6fdef2686ce015c@st.com>
Signed-off-by: Antonio Borneo <e3c49bfed73d0a6201bf9bce92725a03f17606f8@foss.st.com>
Change-Id: I6455c3c740d2e5add28255eb84f8ebaf2870d9d8

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware