ARM: OMAP: pm: fix compilation break

Fix the compilation break observed on latest mainline caused
by 9f97da78 (Disintegrate asm/system.h for ARM):

arch/arm/mach-omap1/pm.c: In function 'omap_pm_prepare':
arch/arm/mach-omap1/pm.c:587: error: implicit declaration of function 'disable_hlt'
arch/arm/mach-omap1/pm.c: In function 'omap_pm_finish':
arch/arm/mach-omap1/pm.c:624: error: implicit declaration of function 'enable_hlt'
arch/arm/mach-omap1/pm.c: In function 'omap_pm_init':
arch/arm/mach-omap1/pm.c:681: error: 'arm_pm_idle' undeclared (first use in this function)
...

arch/arm/mach-omap2/pm.c: In function 'omap_pm_begin':
arch/arm/mach-omap2/pm.c:239: error: implicit declaration of function 'disable_hlt'
arch/arm/mach-omap2/pm.c: In function 'omap_pm_end':
arch/arm/mach-omap2/pm.c:247: error: implicit declaration of function 'enable_hlt'

Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
[tony@atomide.com: updated to fix omap1 too]
Signed-off-by: Tony Lindgren <tony@atomide.com>