spl: armv7m: keep ARM v7M in thumb mode while jumping to entry point

On ARM v7M, the processor will return to ARM mode when executing blx
instruction with bit 0 of the address == 0. Always set it to 1 to stay
in thumb mode.

Similar commit:
f99993c10882f7dc8ec35993d5febe59aac01e6a
Author: Matt Porter <mporter@konsulko.com>
Date:   Tue May 5 15:00:23 2015 -0400
common/cmd_boot: keep ARM v7M in thumb mode during do_go_exec()

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>

common/spl/spl.c

@@ -85,6 +85,9 @@ void spl_set_header_raw_uboot(struct spl_image_info *spl_image)
 {
 	spl_image->size = CONFIG_SYS_MONITOR_LEN;
 	spl_image->entry_point = CONFIG_SYS_UBOOT_START;
+#ifdef CONFIG_CPU_V7M
+	spl_image->entry_point |= 0x1;
+#endif
 	spl_image->load_addr = CONFIG_SYS_TEXT_BASE;
 	spl_image->os = IH_OS_U_BOOT;
 	spl_image->name = "U-Boot";