mach-stm32: Add MPU region for spi-nor memory mapped region

The Quad-SPI interface is able to manage up to 256Mbytes Flash
memory starting from 0x90000000 to 0x9FFFFFFF in the memory
mapped mode.
Add a dedicated MPU region into stm32_region_config.

See application note AN4760 available at www.st.com

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/mach-stm32/soc.c b/arch/arm/mach-stm32/soc.c
index 738305c..6ae31d3 100644
--- a/arch/arm/mach-stm32/soc.c
+++ b/arch/arm/mach-stm32/soc.c
@@ -21,6 +21,9 @@
 		O_I_WB_RD_WR_ALLOC, REGION_16MB },
 #endif
 
+		{ 0x90000000, REGION_1, XN_DIS, PRIV_RW_USR_RW,
+		SHARED_WRITE_BUFFERED, REGION_256MB },
+
 #if defined(CONFIG_STM32F7) || defined(CONFIG_STM32H7)
 		{ 0xC0000000, REGION_0, XN_DIS, PRIV_RW_USR_RW,
 		O_I_WB_RD_WR_ALLOC, REGION_512MB },