V4L/DVB (6569): bt8xx/dst.c: make code static

This patch makes the following needlessly global code static:
- dst_gpio_outb()
- dst_gpio_inb()
- rdc_8820_reset()
- dst_pio_enable()
- dst_command()
- struct tuner_list[]

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>