fbdev: pxafb: use devm_kmemdup*()

Convert to use devm_kmemdup() and devm_kmemdup_array() which are
more robust.

Signed-off-by: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Helge Deller <deller@gmx.de>