ARM: ensure initial page tables are setup for SMP systems

Mapping the same memory using two different attributes (memory
type, shareability, cacheability) is unpredictable.  During boot,
we encounter a situation when we're updating the kernel's page
tables which can lead to dirty cache lines existing in the cache
which are subsequently missed.  This causes stack corruption,
and therefore a crash.

Therefore, ensure that the shared and cacheability settings
matches the configuration that will be used later; this together
with the restriction in early_cachepolicy() ensures that we won't
create a mismatch during boot.

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