V4L/DVB (5457): Dvb-pll: Replace sleep function with a more capable one

The dvb-pll sleep function could only send a 2-byte sequence to the PLL.
This isn't enough in some cases, for example fmd1216me will need to send
a 4-byte command to set both BB and AB to the correct values.

Instead of using a fake band with a frequency of 0 to store the sleep
data (which has room for only two bytes), the new sleep function works
like the init function.  A new pointer is added to the pll description,
and when non-NULL points to a buffer with the length and data to send.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>