ARM: 7453/1: audit: only allow syscall auditing for pure EABI userspace

The audit tools support only EABI userspace and, since there are no
AUDIT_ARCH_* defines for the ARM OABI, it makes sense to allow syscall
auditing on ARM only for EABI at the moment.

Cc: Eric Paris <eparis@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>