SPM: move tfm_arch_is_priv() to generic tfm_arch header

The function tfm_arch_is_priv should not be restricted in
headers that can be used only for v6m/v7m multicore topologies.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: Ia16fda9209fc17c7011ee8bed6ce16b4d60cc364
2 files changed