arm64: mm: Move ASID from TTBR0 to TTBR1

arm64: mm: Move ASID from TTBR0 to TTBR1

commit 7655abb95386 upstream.

In preparation for mapping kernelspace and userspace with different
ASIDs, move the ASID to TTBR1 and update switch_mm to context-switch
TTBR0 via an invalid mapping (the zero page).

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Alex Shi <alex.shi@linaro.org> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@arm.com>
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>