drm/amdgpu: Remove references to struct drm_device.pdev

Using struct drm_device.pdev is deprecated. Convert amdgpu to struct
drm_device.dev. No functional changes.

v3:
	* rebased

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210107080748.4768-3-tzimmermann@suse.de