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: merge redundant hardware.c

hardware.c was defined for both 32 and 64 bit arm kernels. However, the
only difference in the file is the register used in setNextPC. Add this
register as a #define in registerset.h, move hardware.c to be common for
both 32- and 64-bit arm.

style: use consistent styling for all cmake files

Add .cmake-format.yaml which defines custom functions with kwargs to
style nicely

Add a CMake based build system

This commit adds an alternate build system using CMake that operates indepenently of
the existing Kconfig+Kbuild+make based build system