Convert to SPDX license tags

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

Style: Updated style of modified files

Updated the style of various source files recently updated.

libsel4vmmplatsupport: arm PSCI support

Added support for handling arm PSCI calls through the SMC
interface. This brings together SMP support, bringing available
vcpu's online at the request of Linux. The different types of PSCI
calls and return codes are sourced from the ARM Power State
Coordination Interface Design Document (Issue D).

Co-authored-by: Anna Lyons <anna@gh.st>