arm64: Move post_ttbr_update_workaround to C code

We will soon need to invoke a CPU-specific function pointer after changing
page tables, so move post_ttbr_update_workaround out into C code to make
this possible.

Change-Id: Ie58057014bc0c8610ce2f00f09c9f52d28ac49a7
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 95e3de3590e3f2358bb13f013911bc1bfa5d3f53
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[sramana@codeaurora.org: Resolve trivial merge conflicts]
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>