powerpc: book3e_64: fix the align size for paca_struct

powerpc: book3e_64: fix the align size for paca_struct

All the cache line size of the current book3e 64bit SoCs are 64 bytes.
So we should use this size to align the member of paca_struct.
This only change the paca_struct's members which are private to book3e
CPUs, and should not have any effect to book3s ones. With this, we save
192 bytes. Also change it to __aligned(size) since it is preferred over
__attribute__((aligned(size))).

Before:
	/* size: 1920, cachelines: 30, members: 46 */
	/* sum members: 1667, holes: 6, sum holes: 141 */
	/* padding: 112 */

After:
	/* size: 1728, cachelines: 27, members: 46 */
	/* sum members: 1667, holes: 4, sum holes: 13 */
	/* padding: 48 */

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>