kexec: add _ALIGN* marcos for align operation

This patch imports Macros for align operation:
- _ALIGN_UP(addr, size): align addr up on a size boundary
- _ALIGN_DOWN(addr, size): align addr down on a size boundary
- _ALIGN(addr, size): align addr up on a size boundary

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Simon Horman <horms@verge.net.au>