clk: stm32mp1: new compatible for secure RCC support

clk: stm32mp1: new compatible for secure RCC support

Platform STM32MP1 can be used in configuration where some clock
resources cannot be accessed by Linux kernel when executing in non-secure
state of the CPU(s).
In such configuration, the RCC clock driver must not register clocks
it cannot access.
They are expected to be registered from another clock driver such
as the SCMI clock driver.
This change uses specific compatible string "st,stm32mp1-rcc-secure"
to specify RCC clock driver configuration where RCC is secure.

Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@foss.st.com>
Link: https://lore.kernel.org/r/20210617051814.12018-12-gabriel.fernandez@foss.st.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>