arm64: kaslr: defer initialization to initcall where permitted

The early KASLR init code runs extremely early, and anything that could
be deferred until later should be. So let's defer the randomization of
the module region until much later - this also simplifies the
arithmetic, given that we no longer have to reason about the link time
vs load time placement of the core kernel explicitly. Also get rid of
the global status variable, and infer the status reported by the
diagnostic print from other KASLR related context.

While at it, get rid of the special case for KASAN without
KASAN_VMALLOC, which never occurs in practice.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-20-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>