fbdev: atyfb: add stubs for aty_{ld,st}_lcd()

Fix build errors when these functions are not defined.

../drivers/video/fbdev/aty/atyfb_base.c: In function 'aty_power_mgmt':
../drivers/video/fbdev/aty/atyfb_base.c:2002:7: error: implicit declaration of function 'aty_ld_lcd'; did you mean 'aty_ld_8'? [-Werror=implicit-function-declaration]
 2002 |  pm = aty_ld_lcd(POWER_MANAGEMENT, par);
../drivers/video/fbdev/aty/atyfb_base.c:2004:2: error: implicit declaration of function 'aty_st_lcd'; did you mean 'aty_st_8'? [-Werror=implicit-function-declaration]
 2004 |  aty_st_lcd(POWER_MANAGEMENT, pm, par);

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210222032853.21483-1-rdunlap@infradead.org