media: dvb-frontends/dvb-pll: add i2c driver support

registers the module as an i2c driver,
but keeps dvb_pll_attach() untouched for compatibility.

Signed-off-by: Akihiro Tsukada <tskd08@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>