FROMLIST: 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.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git


 commit 400a169447ad2268b023637a118fba27246bcc19)

Change-Id: I4e6edb3dcb6aabe9c17e4698619a093e76495b36
Signed-off-by: Greg Hackmann <ghackmann@google.com>