V4L/DVB (9745): em28xx: Cleanup GPIO/GPO setup code

Cleanup the calls to set the GPIOs and GPOs for various devices,
replacing the register number with the #define from em28xx-reg.h and
converting over to using em28xx_write_reg()

Signed-off-by: Devin Heitmueller <devin.heitmueller@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>