V4L/DVB (4750): AGC command1/2 is board specific

Added config-struct-parameter to take board-specific AGC command 1 and 2 into account.

Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>