Makefile: always preserve output for images that can contain HAB Blocks

Makefile: always preserve output for images that can contain HAB Blocks

The current makefile logic disables creation of the
SPL.log/u-boot-ivt.img.log etc. files when V=1 is given on the command
line, the rationale presumably being that the user wants and gets the
information on the console.

However, from general principles, I don't think a higher V= level
should affect which build artifacts get generated (and certainly
shouldn't produce fewer). Concretely, it's also a problem that when
doing a V=1 build in a terminal, the relevant HAB blocks lines easily
drown in all the other V=1 output.

Moreover, build systems such as Yocto by default pass V=1, so in that
case the information gets hidden away in the do_compile log file, making
it nigh impossible to create a recipe for creating signed U-boot images
- I don't want to disable V=1, because having verbose output in the log
file is valuable when things go wrong, but OTOH trying to go digging in
the do_compile log file (and getting exactly the right lines) is not
pleasant to even think about.

So change the logic so that for V=0, the mkimage output is redirected
to MKIMAGEOUTPUT (which is also the current behaviour), while for any
other value of V, we _additionally_ write the information to make's
stdout, whatever that might be.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Tested-by: Breno Lima <breno.lima@nxp.com>