arm64/kernel: Move 'nokaslr' parsing out of early idreg code

Parsing and ignoring 'nokaslr' can be done from anywhere, except from
the code that runs very early and is therefore built with limitations on
the kind of relocations it is permitted to use.

So move it to a source file that is part of the ordinary kernel build.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20231129111555.3594833-63-ardb@google.com


Signed-off-by: Will Deacon <will@kernel.org>