ARM: at91: pm: Fix rand build error

ARM: at91: pm: Fix rand build error

If ATMEL_PM is y but PM is n, build fails:

arch/arm/mach-at91/pm.c:1435:13: error: redefinition of 'at91rm9200_pm_init'
 void __init at91rm9200_pm_init(void)
             ^~~~~~~~~~~~~~~~~~
In file included from arch/arm/mach-at91/pm.c:29:0:
arch/arm/mach-at91/generic.h:19:27: note: previous definition of 'at91rm9200_pm_init' was here
 static inline void __init at91rm9200_pm_init(void) { }
                           ^~~~~~~~~~~~~~~~~~

ATMEL_PM should not be enabled independently, it is only selected by Soc.

Fixes: f2f5cf78a333 ("ARM: at91: pm: add support for sama5d2 secure suspend")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220517031606.11628-1-yuehaibing@huawei.com
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>