[µTVM] Zephyr: Fix missing board-specific config file in build dir

[gromero]

Hi,

Could the following small change be reviewed please?

It's necessary to make the build of the libraries (common, utvm_rpc_common, utvm_rpc_server, etc) be aware of board-specific config settings, like per board CONFIG_FPU (since some boards, like mps2, don't have a FPU and currently it's set globally in prj.conf). It's also necessary to move forward the following PR:
#8055

Without that change, for instance, even if CONFIG_FPU=y is set in the board config file (like boards/qemu_x86.conf) the libraries are built against soft-float because CONFIG_FPU=y doesn't take effect and so running some models that rely on float point will fail.

This happens because currently board-specific config files (boards/*.conf) are not
copied from Zephyr project dir to the destination build dir, so
as a consequence the per board configs are not used when building
the runtime libraries, like libcommon. Hence, for instance, it's
currently not possible to set CONFIG_FPU per board since it only
takes effect when it's set in the generic 'prj.con' config file.

This commit fixes it by copying to the build dir, to each lib
dir, the proper .conf for the selected target board. For example,
if target 'qemu_x86' is selected 'qemu_x86.conf' is copied to
the boards/ dir inside the lib dirs, so Zephyr build system can
find it and combine it with configs found in the generic 'prj.conf'.

Thanks & best regards,
Gustavo

[gromero]

@areusch Hi! Any clue if the CI error is legit or not? Seems quite unrelated to my change. I don't have a GPU to try it out locally unfortunately so I'll need a hand to figure it out : )

[areusch]

thanks @gromero , hopefully Project API will obviate this change since we'll just be using a single project, but let's merge in the meantime. unfortunately the CI error looks unrelated/flaky, can you just push an empty commit or git commit --amend to retrigger?