ARM: SAMSUNG: Fixup endian issues in CPU detection

If the system is built for big endian, then the CPU identificaiton register
will be read in the wrong order. Fix this by using readl_relaxed() on the
register.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>