hsi: Build hsi_boardinfo.c into hsi core if enabled

If the HSI core is built as a module hsi_boardinfo may still
be built-in as its Kconfig type is bool, which can cause build
issues. Fix this by building this code into the HSI core when
enabled.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>