ARM: at91: pm: move SAM9X60's PM under its own SoC config flag

Move SAM9X60's PM part under SoC config flag. This allows the building
of SAM9X60 platform withouth depending on CONFIG_SOC_AT91SAM9 flag,
allowing us to select only necessary config flags for SAM9X60.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1575035505-6310-4-git-send-email-claudiu.beznea@microchip.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>