drm/amd/amdgpu: fix build failure due to implicit declaration

The builds for alpha and mips allmodconfig fails with the error:

  drivers/gpu/drm/amd/amdgpu/psp_v13_0.c:534:23: error: implicit declaration of function 'vmalloc'; did you mean 'kvmalloc'? [-Werror=implicit-function-declaration]
  drivers/gpu/drm/amd/amdgpu/psp_v13_0.c:534:21: error: assignment to 'void *' from 'int' makes pointer from integer without a cast [-Werror=int-conversion]
  drivers/gpu/drm/amd/amdgpu/psp_v13_0.c:545:33: error: implicit declaration of function 'vfree'; did you mean 'kvfree'? [-Werror=implicit-function-declaration]

Add the header file for vmalloc and vfree.

Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>