Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

arm: remote IPI call support for VIRQS

Added support for injecting remote IPI calls towards given VCPU's
on SMP configured systems. This introudcing a new type of
IpiRemoteCall and handlers for updating the vgic state on
incoming/outgoing IPI's.

Co-authored-by: Yanyan Shen <yanyan.shen@data61.csiro.au>

Explicit casts between enum types in IPI

Depending on the platform, IPI has a slightly different interface.
Explicitly cast from the more speific enum type to the generic
and vice versa when calling in and out of generic code.

Another possibility would be to typedef a specific enum on RISCV
platforms that aliases the one currently used. Then casting would only
have to take place when passing args to function calls.

arm,SMP: Refactor irq_t structure for smp

Explicitly create a struct definition for irq_t on SMP Arm
configurations. This makes it a lot harder to mistakenly use the wrong
irq encoding when moving an irq between a cnode index and hardware irq
number / core. A couple areas where this was being handled incorrectly
was fixed as part of the refactor. When performing an ipi for masking
PPI interrupts, the idx encoding is used as it fits into a single word.

[SMP] New IPI call to unmask remote IRQ

Added a new IPI on ARM to unmask a remote private interrupt.

arm: Call local TLB functions in IPI handlers.

ARM/SMP: Guard FPU operations

SMP: Introduce ENABLE_SMP_SUPPORT

- Make it more readable and less confusing compared to the 'CONFIG_MAX_NUM_NODES > 1' check

SELFOUR-806: ARM/SMP/FPU - Support remote FPU switch

trivial: fixes to popcountl implementation

SELFOUR-746: IPI Handler for ARM

SMP/ARM: include generic smp/ipi.h and move ipi.c to smp/