feat(stm32mp2): add a runtime service for STGEN configuration

Other component such as OP-TEE may have the responsibility for
STGEN configuration but updating Arm CNTFRQ can only be done from
EL3. Therefore, implement a SiP SMC handler for this purpose and
a runtime service to catch SIP SMCs.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Signed-off-by: Maxime Méré <maxime.mere@foss.st.com>
Change-Id: I7854e1ae6328f149798b43d52bb1ecdf71a5aa69
5 files changed