x86: relocate_kernel - use predefined PAGE_SIZE instead of own alias

This patch does clean up relocate_kernel_(32|64).S a bit by getting rid
of local PAGE_ALIGNED macro. We should use well-known PAGE_SIZE instead

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>