clarify license for generated headers

Invocation and syscall headers are generated and provided under
BSD-2-Clause for user code and GPL-2.0-only for kernel code. To
facilitate people other than the copyright holder performing this
operation, the master files are provided under both (BSD or GPL, free
to choose).

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.

python2 --> python3

Update all scripts and build system to call python3, given python2's
upcoming doom. Use sys.maxsize instead of sys.maxint in one script
(maxint does not exist in python3).

style: run autopep8 on python files

tools: State jinja2 version

Provides a graceful error when jinja2 is the wrong version

Remove references to unused tempita library

tools: Fix whitespace differences in header gen

libsel4: change tempita to jinja2

tools: fix licenses

libsel4: fix licenses

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

tools: Correct case where label numbers will be 0

If `seL4_arch_invocations` is an empty list, this will cause `nSeL4ArchInvocationLabels`
to be declared as 0, rather than `nInvocationLabels` as intented. This change correctly
respects the behaviour of the 'first' variable, and does an explicit assignment to
`nSeL4ArchInvocationLabels` should it be the first (and only) member of the enum.

Closes #53

update #ifdef to #if in auto generated files

tools: Remove arithmetic in invocation generation

If invocations are hidden behind config guards the count of how
many invocations there are will be wrong. The C compiler will
correctly assign the value with enum auto numbering, so there's
no need to override that here

tools: emit error if first invocation conditional

Placing a config condition on the first define
in sel4arch.xml will fail as currently the first define
must start at the last define + 1 of the previous
invocation enum.

If this is ever required, autoconf.h will need to be passed
to the script so it can check config variables itself.

tools: add conditional invocation label defines

tools: add conditional invocation label defines

tools: invocation_header_gen: python3 compat

tools: invocation_header_gen: remove trailing whitespace

libsel4: Explicitly generate number of invocation labels to handle case where there are no invocations

libsel4: Generate libsel4 definitions from the current ARCH as well as the SEL4_ARCH

Use usr/bin/env for all python bangpaths to enable virtualenv use.

Very useful with python3 as the default platform.

Release snapshot