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.

fastpath: reorganize the code layout on ARM

fastpath_call and fastpath_reply_recv got inlined into a single
function. This could cause loading unused code in cache and
additional jump instructions required in c_handle_syscall.

mcs: scheduling context donation over ipc

After this commit, threads blocked on an endpoint can recieve a
scheduling context from the thread that wakes the blocked thread.

Consistent naming of FaultIP and NextIP in kernel

Always refer to the virtual register that stores the address of a fault
as FaultIP and the register that stores the return for a fault NextIP.

aarch64: ERET from TX2 SErrors

Ignore system errors reported on TX2 at the moment.

armv8: Add HVC64 and VCPU faults handlers for EL2.

armv8: Load kernel stack in invalid_vector_entry

The halt may call printf, so we set up the kernel stack.

armv8: Load kernel stack in cur_el_sync

The halt may call printf, so we set up the kernel stack.

armv8: Add ELR, ESR, SPSR, and TPIDR for EL2

armv8: Generalise label names for EL1/2

armv8: Introduce ELR, ESR, SPSR, and TPIDR for EL1

armv8: Generalise ESR shift and constants

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

Fix licenses (the rest)

aarch64: FPU lazy context switch

aarch64: Initial implementation

aarch64: add preliminary folders and Makefiles