board: stemmy: Increase boot image to 64 MB

When using a recent kernel with a bunch of compiled-in
stuff the kernel image easily becomes bigger than 8 MB
yielding this error:

  Loading Kernel Image
  Image too large: increase CONFIG_SYS_BOOTM_LEN
  Must RESET board to recover

Fix this by bumping to SZ_64MB.

Cc: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
diff --git a/include/configs/stemmy.h b/include/configs/stemmy.h
index e5571b2..96e759d 100644
--- a/include/configs/stemmy.h
+++ b/include/configs/stemmy.h
@@ -14,6 +14,7 @@
  * bootloader. New images are loaded at the same address for compatibility.
  */
 #define CONFIG_SYS_INIT_SP_ADDR		CONFIG_SYS_TEXT_BASE
+#define CONFIG_SYS_BOOTM_LEN		SZ_64M
 
 /* FIXME: This should be loaded from device tree... */
 #define CONFIG_SYS_L2_PL310