intc/arm_gic: Refactor secure/ns access check in the CPU interface

intc/arm_gic: Refactor secure/ns access check in the CPU interface

An access to the CPU interface is non-secure if the current GIC instance
implements the security extensions, and the memory access is actually
non-secure. Until then, it was checked with tests such as
  if (s->security_extn && !attrs.secure) { ... }
in various places of the CPU interface code.

With the implementation of the virtualization extensions, those tests
must be updated to take into account whether we are in a vCPU interface
or not. This is because the exposed vCPU interface does not implement
security extensions.

This commits replaces all those tests with a call to the
gic_cpu_ns_access() function to check if the current access to the CPU
interface is non-secure. This function takes into account whether the
current CPU is a vCPU or not.

Note that this function is used only in the (v)CPU interface code path.
The distributor code path is left unchanged, as the distributor is not
exposed to vCPUs at all.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180727095421.386-9-luc.michel@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>