ARM: imx: set cache line size to 64 bytes for i.MX5

The core of i.MX5 series is cortex-A8, its cache line size is 64 bytes
instead of 32 bytes. Refer to the OMAP3's selection, we choose 64
bytes for i.MX5, this can increase a little bit performance when
perform cache operations.

Signed-off-by: Jason Wang <jason77.wang@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>