imx: add macro to detect whether USB has been initialized

This macro allows to detect whether the boot ROM initialized USB
already (serial downloader). This is helpful to reliably detect
if the system has been recovered via USB serial downloader.
Signed-off-by: NStefan Agner <stefan.agner@toradex.com>
Acked-by: NMarcel Ziswiler <marcel.ziswiler@toradex.com>

arch/arm/include/asm/arch-mx6/imx-regs.h

@@ -996,5 +996,12 @@ struct pwm_regs {
 	u32	pr;
 	u32	cnr;
 };
+
+/*
+ * If ROM fail back to USB recover mode, USBPH0_PWD will be clear to use USB
+ * If boot from the other mode, USB0_PWD will keep reset value
+ */
+#define	is_boot_from_usb(void) (!(readl(USB_PHY0_BASE_ADDR) & (1<<20)))
+
 #endif /* __ASSEMBLER__*/
 #endif /* __ASM_ARCH_MX6_IMX_REGS_H__ */