[media] media: s5p-hdmi: add HPD GPIO to platform data

This patch extends s5p-hdmi platform data by a GPIO identifier for
Hot-Plug-Detection pin.

Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>