board: stm32mp1: support boot from spi-nand

Manage BOOT_FLASH_SPINAND, with boot_device="spi-nand"
and treat this value in bootcmd_stm32mp.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/mach-stm32mp/include/mach/stm32.h b/arch/arm/mach-stm32mp/include/mach/stm32.h
index 76d593d..242bacc 100644
--- a/arch/arm/mach-stm32mp/include/mach/stm32.h
+++ b/arch/arm/mach-stm32mp/include/mach/stm32.h
@@ -80,6 +80,9 @@
 
 	BOOT_SERIAL_USB = 0x60,
 	BOOT_SERIAL_USB_OTG = 0x62,
+
+	BOOT_FLASH_SPINAND = 0x70,
+	BOOT_FLASH_SPINAND_1 = 0x71,
 };
 
 /* TAMP registers */