media: platform: rename mediatek/mtk-jpeg/ to mediatek/jpeg/

As the end goal is to have platform drivers split by vendor,
rename mediatek/mtk-jpeg/ to mediatek/jpeg/.

Requested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>