ARM: mx53: Allow suspend/resume

Current imx53_pm_init() implementation is incomplete as it lacks calling
suspend_set_ops().

Use a single imx5_pm_init() function to handle both mx51 and mx53.

This allows mx53 to enter in low-power mode.

Tested on a mx53qsb:

root@freescale /$ echo mem > /sys/power/state
PM: Syncing filesystems ... done.
mmc0: card e624 removed
Freezing user space processes ... (elapsed 0.001 seconds) done.
Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
Suspending console(s) (use no_console_suspend to debug)

... (Press Power button)

PM: suspend of devices complete after 17.067 msecs
PM: suspend devices took 0.020 seconds
PM: late suspend of devices complete after 0.954 msecs
PM: noirq suspend of devices complete after 1.288 msecs
Disabling non-boot CPUs ...
PM: noirq resume of devices complete after 0.680 msecs
PM: early resume of devices complete after 0.914 msecs
PM: resume of devices complete after 44.955 msecs
PM: resume devices took 0.050 seconds
Restarting tasks ... done.
mmc0: host does not support reading read-only switch. assuming write-enable.
mmc0: new SDHC card at address e624
mmcblk0: mmc0:e624 SU04G 3.69 GiB
 mmcblk0: p1 p2 p3
libphy: 63fec000.etherne:00 - Link is Down
libphy: 63fec000.etherne:00 - Link is Up - 100/Full
root@freescale /$

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>