feat(stm32mp1): rework SVC services

Having two generations of STM32MPX using the same SMCCC protocol,
rework the SVC services setup to put in common what can be put
in common and implement platform-specific handlers.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Signed-off-by: Maxime Méré <maxime.mere@foss.st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I000573e50d55dc70163c2657c12cc84085416f6b
6 files changed