replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

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: CONFIG_L1_CACHE_LINE_SIZE_BITS in cmake

Move definition of L1_CACHE_LINE_SIZE_BITS to cmake where it is set
according to the arm processor family.

This removes duplication in the hardware.h header files and makes adding
a new processor family require less lines changed.

Remove symlinked libsel4 files from include dir

These files can be included normally using libsel4 include paths. This
removes situations where the same file is available under different
include paths due to symlinking into different directory structures.

style: consistently attach return type

Add attach-return-type to astyle

armv8: Add SCTLR EL1 stack alignment check field.

armv8: add macro L1_CACHE_LINE_SIZE for aarch64

Fix licenses (the rest)

Use CONFIG_ variables instead of configuration definitions

s/D61/DATA61/ in license headers for consistency

plat: add tx1 support

aarch64: Initial implementation

aarch64: add preliminary folders and Makefiles