arm64: entry: Make the trampoline cleanup optional

commit d739da1694a0eaef0358a42b76904b611539b77b upstream.

Subsequent patches will add additional sets of vectors that use
the same tricks as the kpti vectors to reach the full-fat vectors.
The full-fat vectors contain some cleanup for kpti that is patched
in by alternatives when kpti is in use. Once there are additional
vectors, the cleanup will be needed in more cases.

But on big or little systems, the cleanup would be harmful if no
trampoline vector were in use. Instead of forcing CPUs that don't
need a trampoline vector to use one make the trampoline cleanup
optional.

Entry at the top of the vectors will skip the cleanup. The trampoline
vectors can then skip the first instruction, triggering the cleanup
to run.

Change-Id: I1db4a6bc057f191cd596e6cd68d50f6a26a4eddf
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: 87eccd56
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Kishor Krishna Bhat <quic_kishkris@quicinc.com>