[ARM] 4489/1: pxa: split pxa_cpu_suspend to processor specific ones

1. split pxa_cpu_suspend to pxa25x_cpu_suspend and pxa27x_cpu_suspend
   and make pxa25x_cpu_pm_enter() and pxa27x_cpu_pm_enter() to invoke
   the corresponding _suspend functions, thus remove all those ugly
   #ifdef .. #endif out of sleep.S

2. move the declarations of those suspend functions to pm.h

note: this is not a clean enough solution until all the pxa25x and
pxa27x specific part is further removed out of sleep.S, sleep.S is
supposed to contain generic code only

Signed-off-by: eric miao <eric.y.miao@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>