drm/amd/powerplay: reshuffle headers to make pr_fmt macro before <linux/xxx.h>

This patch reshuffles headers to define pr_fmt before <linux/xxx.h>.
It can avoid pr_fmt redefine warnning from linux/xxx.h like below:

CC [M]  /home/ray/gpu/BUILD/x86_64/linux/drivers/gpu/drm/amd/amdgpu//../powerplay/amd_powerplay.o
/home/ray/gpu/BUILD/x86_64/linux/drivers/gpu/drm/amd/amdgpu//../powerplay/amd_powerplay.c:24:0: warning: "pr_fmt" redefined
 #define pr_fmt(fmt) "[powerplay] " fmt
 ^
In file included from include/linux/kernel.h:13:0,
                 from include/linux/list.h:8,
                 from include/linux/agp_backend.h:33,

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>