rockchip: rk3528: Implement read_brom_bootsource_id()

The bootsource ids reported by BootROM of RK3528 for e.g. USB differs
compared to prior SoCs:

- Booting from USB report a new bootsource id 0x81.

Add a RK3528 specific read_brom_bootsource_id() function to help decode
this new bootsource id value to help support booting from USB on RK3528.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

arch/arm/mach-rockchip/rk3528/rk3528.c

@@ -49,6 +49,21 @@ void board_debug_uart_init(void)
 {
 }
 
+u32 read_brom_bootsource_id(void)
+{
+	u32 bootsource_id = readl(BROM_BOOTSOURCE_ID_ADDR);
+
+	/* Re-map the raw value read from reg to an existing BROM_BOOTSOURCE
+	 * enum value to avoid having to create a larger boot_devices table.
+	 */
+	if (bootsource_id == 0x81)
+		return BROM_BOOTSOURCE_USB;
+	else if (bootsource_id > BROM_LAST_BOOTSOURCE)
+		log_debug("Unknown bootsource %x\n", bootsource_id);
+
+	return bootsource_id;
+}
+
 int arch_cpu_init(void)
 {
 	u32 val;