Platform/RaspberryPi: Normal memory should not be marked as uncached

The EFI spec seems to indicate that the EFI uncacheable attribute
should be mapped to device memory rather than normal-nc. This means
that the UEFI mem attribute for the >3G ram doesn't match the remainder
of the RAM in the machine.

So, lets remove the uncacheable attribute to make it more consistent.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>