amdkfd build regression if HSA_AMD is disabled

[StDenis, Tom]

Hi All,

The commit:

commit 62f65d3cb34a8300bf1e07fc478e03c3c02634d4
Refs: v4.20-rc3-524-g62f65d3cb34a
Author:     Felix Kuehling <Felix.Kuehling at amd.com>
AuthorDate: Mon Nov 19 20:05:54 2018 -0500
Commit:     Felix Kuehling <Felix.Kuehling at amd.com>
CommitDate: Fri Dec 7 17:17:11 2018 -0500

     drm/amdgpu: Add KFD VRAM limit checking

     We don't want KFD processes evicting each other over VRAM usage.
     Therefore prevent overcommitting VRAM among KFD applications with
     a per-GPU limit. Also leave enough room for page tables on top
     of the application memory usage.

     Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
     Reviewed-by: Eric Huang <JinHuiEric.Huang at amd.com>
     Acked-by: Alex Deucher <alexander.deucher at amd.com>

Breaks the build if HSA_AMD is not enabled:

scripts/kconfig/conf  --syncconfig Kconfig
   DESCEND  objtool
   CALL    scripts/checksyscalls.sh
   CHK     include/generated/compile.h
   Building modules, stage 2.
   MODPOST 63 modules
Kernel: arch/x86/boot/bzImage is ready  (#58)
ERROR: "amdgpu_amdkfd_unreserve_memory_limit" 
[drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
make: *** [Makefile:1271: modules] Error 2

This is because the function being used is not included in the build 
(the previous function called was part of amdgpu_amdkfd.c which is 
unconditionally built).

Cheers,
Tom