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: optionally pass bootloader DTB to userspace

We now support receiving a DTB from the ELF loader and passing it on
to userspace in extra bootinfo. We still support booting without a DTB,
though - the device tree address is set to zero in the boot code and no
extra bootinfo region is provided.

armv8: Store stack and core ID to TPIDR_EL2 in EL2.

aarch64: Init SCTLR_ELn and use SP_ELn.

When the kernel is running in EL2, we need to initialise the
SCTLR_EL2. We also ensure that SP_EL1 or SP_EL2 is used as
kernel stack pointer based on the current running EL.

armv8: Add SMP support for aarch64

(1) Use NODE_STATE() to access per-core kernel data.
(2) Allocate kernel stack in src/arch/arm/64/head.S.
(3) Use the TPIDR_EL1 to contain the kernel stack pointer
as well as the logical core ID. The kernel stack must
be 4-KiB aligned, and the lowest 12 bits of TPIDR_EL1
are for the logical core ID.
(4) Define the LD_EX, ST_EX, and OP_WIDTH as "ldxr", "stxr",
and "w".
(5) Add irq_remote_call_ipi and irq_reschedule_ipi

SMP: Introduce ENABLE_SMP_SUPPORT

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

Fix licenses (the rest)

ARM: Fix assembler error with BIT definition

[SELFOUR-744]: Modify head.S to load stacks for each core and implement getCurrentCPUIndex

ARM: use restore_user_context() in head.S

aarch64: reset the el0 stack alignment checking

aarch64: Initial implementation

aarch64: add preliminary folders and Makefiles