spl: riscv: opensbi: Error on misaligned FDT

libfdt 1.6.1+ requires the FDT to be 8-byte aligned and returns an error
if not. OpenSBI 1.0+ includes this version of libfdt and will also
reject misaligned FDTs.

However, OpenSBI cannot indicate the error to the user: since it cannot
access the serial console, it can only silently hang. This proved very
difficult to diagnose without proper debugging facilities. Therefore,
give the U-Boot SPL, which *can* print error messages, an additional
check for proper FDT alignment. Hopefully this saves a lot of
development cycles if another developer encounters alignment problems.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>

common/spl/spl_opensbi.c

@@ -57,6 +57,11 @@ void __noreturn spl_invoke_opensbi(struct spl_image_info *spl_image)
 		hang();
 	}
 
+	if (!IS_ALIGNED((uintptr_t)spl_image->fdt_addr, 8)) {
+		pr_err("SPL image loaded an improperly-aligned device tree\n");
+		hang();
+	}
+
 	/*
 	 * Originally, u-boot-spl will place DTB directly after the kernel,
 	 * but the size of the kernel did not include the BSS section, which