drm/amd/amdgpu/amdgpu_kms: Remove 'struct drm_amdgpu_info_device dev_info' from the stack

Place it on the heap instead.

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c: In function ‘amdgpu_info_ioctl’:
 drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c:979:1: warning: the frame size of 1128 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>