ARM: 6866/1: Do not restrict HIGHPTE to !OUTER_CACHE

The HIGHPTE config option depends on !OUTER_CACHE. However, there is no
set_pte_ext() function that does outer cache maintenance by physical
address, hence no need for such restriction.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>