Cleanup u-boot-tools

[bapt]

Summary

• Do not overwrite do-build it is not necessary
• Ensure the env variables are respected during configure phase
• Now that we use the regular do-build kernel we can pass gmake variables via arguments which allows to overwrites predefine ones without custom patches
• Force verbose mode when building to see what command line is invoke, in in particular which compiler is called
• Overwrite NOSTDINC_FLAGS because on freebsd we do actually want to use our regular standard include files