panfrost: make mediatek_mt8183_supplies and mediatek_mt8183_pm_domains static

This symbol is not used outside of panfrost_drv.c, so marks it static.

Fix the following sparse warning:

drivers/gpu/drm/panfrost/panfrost_drv.c:641:12: warning: symbol
'mediatek_mt8183_supplies' was not declared. Should it be static?

drivers/gpu/drm/panfrost/panfrost_drv.c:642:12: warning: symbol
'mediatek_mt8183_pm_domains' was not declared. Should it be static?

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1631956414-85412-1-git-send-email-jiapeng.chong@linux.alibaba.com