i2c-pxa: Remove hardcoded #ifdef and use cpu_is_pxa27x

remove #ifdef CONFIG_PXA27x .. #endif and use cpu_is_pxaXXXX() macros
so that a single binary can support PXA25x/PXA27x/PXA3xx at run-time.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>