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: New virtual PPI event fault type

This commit introduces a new fault type, seL4_Fault_VPPIEvent.

This change means the kernel can reserve PPI interrupts and virtualise
them via delivering the irq to the active vcpu through a
specific fault. This enables multiplexing PPI IRQs across multiple VCPUS
which requires correctly masking and unmasking the IRQ depending on
which VCPU is running.

A new VCPU invocation, seL4_ARM_VCPU_AckVPPI is also added for
acknowledging the handling of the IRQ. This takes an IRQ as a parameter
but will only accept IRQ numbers that are sent as VPPIEvent faults.

Co-authored-by: Rafal Kolanski <rafal.kolanski@data61.csiro.au>
Co-authored-by: Kent McLeod <Kent.Mcleod@data61.csiro.au>

mcs: add seL4_SchedContext_YieldTo

Implement seL4_SchedContext_YieldTo, which allows users to manipulate
the scheduling queues up to their MCP and can be used for user level
scheduling.

mcs: timeout exceptions

- Add seL4_TCB_SetTimeoutEndpoint
- implement timeout exceptions

style: consistently attach return type

Add attach-return-type to astyle

libsel4: fix licenses

- some were incorrectly marked GPL (libsel4 is BSD)
- update NICTA --> DATA61 etc
- fix tags D61 --> DATA61
- update year to 2017

s/D61/DATA61/ in license headers for consistency

libsel4: Optional public symbols for external interfaces

CONFIG_LIB_SEL4_PUBLIC_SYMBOLS=y will disable inlining for external
interfaces (except deprecated functions), thereby providing public
symbols for easy linkage with other languages.

libsel4: Correct VGIC and VCPU fault types

SELFOUR-413: refactor libsel4 fault API

This is a *breaking API change*

This commit:

* makes seL4_Fault_tag_t common between the kernel and libsel4
* deprecates the existing functions from sel4/messages.h includes
* introduces a new fault API in sel4/faults.h and
* sel4/sel4_arch/faults.h
* deprecates seL4_GetTag(), as the function did not work without
the user calling seL4_SetTag() first (seL4_MessageInfo is passed
in registers and not set in the IPC buffer)
* removes previously deprecated functions (deprecated prior to 3.0.0)
* updates the seL4 manual to reflect the changes