arm64: Extract early FDT mapping from kaslr_early_init()

mainline inclusion
from mainline-v5.12-rc1
commit f6f0c436
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7ZC0H

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f6f0c4362f070cab4a0cec432e82428d702ce0a6



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As we want to parse more options very early in the kernel lifetime,
let's always map the FDT early. This is achieved by moving that
code out of kaslr_early_init().

No functional change expected.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: David Brazdil <dbrazdil@google.com>
Link: https://lore.kernel.org/r/20210208095732.3267263-13-maz@kernel.org


[will: Ensue KASAN is enabled before running C code]
Signed-off-by: Will Deacon <will@kernel.org>

Conflicts:
	arch/arm64/include/asm/setup.h
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>