ARM: lpc32xx: Use kmemdup to replace duplicating its implementation

kmemdup is better than kmalloc() + memcpy(), and we do not like
open code. So just use kmemdup instead.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
[vzapolskiy: resolved a merge conflict]
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>