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.

imx8mq-evk: initial support for aarch32

Add initial i.MX8M Quad evk 64-bit Support

This adds support for the 64-bit i.MX8M Quad evaluation kit.
Currently only AArch64 EL1 is supported.