stm32mp: add syscon for STGEN

Add STGEN as SYSCON device: allow access to device address
defined in device tree

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/mach-stm32mp/include/mach/stm32.h b/arch/arm/mach-stm32mp/include/mach/stm32.h
index 40faeb0..c7a2789 100644
--- a/arch/arm/mach-stm32mp/include/mach/stm32.h
+++ b/arch/arm/mach-stm32mp/include/mach/stm32.h
@@ -25,6 +25,11 @@
 #define STM32_DDR_SIZE			SZ_1G
 
 #ifndef __ASSEMBLY__
+/* enumerated used to identify the SYSCON driver instance */
+enum {
+	STM32MP_SYSCON_UNKNOWN,
+	STM32MP_SYSCON_STGEN,
+};
 
 /*
  * enumerated for boot interface from Bootrom, used in TAMP_BOOT_CONTEXT