ARM: at91: pm: Add Backup mode for SAMA7D65

Add config check that enables Backup mode for SAMA7D65 SoC.

Add SHDWC_SR read to clear the status bits once finished exiting backup
mode. This is only for SAMA7D65 SoCs. The SHDWC status register
needs to be cleared after exiting backup mode to clear the wake up pin
status.

Signed-off-by: Ryan Wanner <Ryan.Wanner@microchip.com>
Link: https://lore.kernel.org/r/3a1f59af1ac9322b0203694b535d5d13120a31eb.1740671156.git.Ryan.Wanner@microchip.com
[claudiu.beznea: dropped extra blank lines, use {} for multi-line
 statements that includes comments, s/PM/pm in commit title to have the
 same pattern accross all commits]
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>

Author: ryan-wanner

arch/arm/mach-at91/pm.c

@@ -647,6 +647,11 @@ static void at91_pm_suspend(suspend_state_t state)
 		at91_suspend_sram_fn = fncpy(at91_suspend_sram_fn,
 					     &at91_pm_suspend_in_sram,
 					     at91_pm_suspend_in_sram_sz);
+
+		if (IS_ENABLED(CONFIG_SOC_SAMA7D65)) {
+			/* SHDWC.SR */
+			readl(soc_pm.data.shdwc + 0x08);
+		}
 	} else {
 		at91_suspend_finish(0);
 	}
@@ -1065,7 +1070,8 @@ static int __init at91_pm_backup_init(void)
 	int ret = -ENODEV, located = 0;
 
 	if (!IS_ENABLED(CONFIG_SOC_SAMA5D2) &&
-	    !IS_ENABLED(CONFIG_SOC_SAMA7G5))
+	    !IS_ENABLED(CONFIG_SOC_SAMA7G5) &&
+	    !IS_ENABLED(CONFIG_SOC_SAMA7D65))
 		return -EPERM;
 
 	if (!at91_is_pm_mode_active(AT91_PM_BACKUP))