ARM: mx5: use generic irq chip pm interface for pm functions on

Two problems exist in the current i.MX5 pm suspend/resume and idle
functions. The first is the current i.MX5 suspend routine will call
tzic_enable_wake(1) to set wake source, this will set all enabled
irq as wake source rather than those wake capable. The second
is i.MX5 idle will call mx5_cpu_lp_set() to prepare enter low power
mode, but it forgets to call wfi instruction to enter this mode.

To fix these two problems, using generic irq chip pm interface and
modify function imx5_idle().

[Tested by Shawn Guo on imx51 babbage board.
 Tested by Hui Wang on imx51 pdk board.]

Signed-off-by: Hui Wang <jason77.wang@gmail.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>