ARM: at91: pm: add quirk for sam9x60's ulp1

On SAM9X60 2 nop operations has to be introduced after setting
WAITMODE bit in CKGR_MOR.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1579522208-19523-9-git-send-email-claudiu.beznea@microchip.com

arch/arm/mach-at91/pm_suspend.S

@@ -275,6 +275,10 @@ ENDPROC(at91_backup_mode)
 	orr	tmp1, tmp1, #AT91_PMC_KEY
 	str	tmp1, [pmc, #AT91_CKGR_MOR]
 
+	/* Quirk for SAM9X60's PMC */
+	nop
+	nop
+
 	wait_mckrdy
 
 	/* Enable the crystal oscillator */