refactor(stm32mp15-fdts): remove RCC secure-status

The RCC security is managed with a dedicated compatible:
"st,stm32mp1-rcc-secure" [1].
Remove useless secure-status property in boards rcc nodes.

[1] 812daf916c ("feat(st): update the security based on new compatible")

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Iff31044ade78dd9c432120dce65375fe2b0d36d6
7 files changed