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>

Documentation/DocBook/device-drivers.tmpl

@@ -511,7 +511,7 @@ X!Ilib/fonts/fonts.c
      </para>
 
 !Iinclude/linux/hsi/hsi.h
-!Edrivers/hsi/hsi.c
+!Edrivers/hsi/hsi_core.c
   </chapter>
 
   <chapter id="pwm">