stm32mp: Fix board_get_usable_ram_top()

mmu_set_region_dcache_behaviour() parameters must be aligned
which is not always the case.
For example for STM32MP2, we stayed stuck inside
mmu_set_region_dcache_behaviour() in an infinite loop because
set_one_region() always return 0 due to start parameter which is
not aligned.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/arch/arm/mach-stm32mp/dram_init.c b/arch/arm/mach-stm32mp/dram_init.c
index b061057..34b958d 100644
--- a/arch/arm/mach-stm32mp/dram_init.c
+++ b/arch/arm/mach-stm32mp/dram_init.c
@@ -81,7 +81,7 @@
 	/* add 8M for U-Boot reserved memory: display, fdt, gd,... */
 	size = ALIGN(SZ_8M + CONFIG_SYS_MALLOC_LEN + total_size, MMU_SECTION_SIZE);
 
-	reg = gd->ram_top - size;
+	reg = ALIGN(gd->ram_top - size, MMU_SECTION_SIZE);
 
 	/* Reserved memory for OP-TEE at END of DDR for STM32MP1 SoC */
 	if (IS_ENABLED(CONFIG_STM32MP13X) || IS_ENABLED(CONFIG_STM32MP15X)) {