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 <[e-mail]>
Signed-off-by: Andrew F. Davis <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

Documentation/DocBook/device-drivers.tmpl

···
      </para>
 
 !Iinclude/linux/hsi/hsi.h
-!Edrivers/hsi/hsi.c
+!Edrivers/hsi/hsi_core.c
   </chapter>
 
   <chapter id="pwm">

drivers/hsi/Makefile

···
 #
 # Makefile for HSI
 #
-obj-$(CONFIG_HSI_BOARDINFO)	+= hsi_boardinfo.o
 obj-$(CONFIG_HSI)		+= hsi.o
+hsi-objs			:= hsi_core.o
+hsi-$(CONFIG_HSI_BOARDINFO)	+= hsi_boardinfo.o
 obj-y				+= controllers/
 obj-y				+= clients/