[U-Boot] logo part Makefile doesn't work as expected

[Bo Shen]

Hi Masahiro Yamada,
   Today, I tested with u-boot master branch, I found the u-boot logo is 
not set as we expected. The following line's do not executed as 
expected, as the BOARD and VENDOR parameter value is not passed to 
<tools/Makefile>. So, if not define LOGO_BMP, it always take the first 
value.
   I try some method to fix it, it works, however I am not familiar with 
whole build system, so can you help to fix it? Thanks.

--->8---
# Generic logo
ifeq ($(LOGO_BMP),)
LOGO_BMP= $(srctree)/$(src)/logos/denx.bmp

# Use board logo and fallback to vendor
ifneq ($(wildcard logos/$(BOARD).bmp),)
LOGO_BMP= $(srctree)/$(src)/logos/$(BOARD).bmp
else
ifneq ($(wildcard logos/$(VENDOR).bmp),)
LOGO_BMP= $(srctree)/$(src)/logos/$(VENDOR).bmp
endif
endif
---8<---

Best Regards,
Bo Shen