Make SMCCC usable by device drivers

To allow device drivers to call into SMCCC we need to initialise it
earlier. As it depends on PSCI, and that is detected via ACPI or FDT
move the call to smccc_init to the PSCI driver.

Add a function for drivers to read the smccc version, or 0 if smccc
is not present.

(cherry picked from commit 0600af1ff16041f15633b2263a8ad9525eecd2f1)
(cherry picked from commit 7ca55fcc541b375c83eaf75f0658b79f250c82fd)