CLeanup u-boot-tools

• 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
• Register the dependency on libssl/libcrypto

Approved by: manu
Differential Revision: https://reviews.freebsd.org/D13543