ARM: sun9i: smp: Add is_a83t field

To prepare the support of sun8i-a83t, add a field in the smp_data
structure to know if we are on sun9i-a80 or sun8i-a83t.

Add also a global variable to retrieve which architecture we are
having.

Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>