V4L/DVB (4961): Add support for the ASUS P7131 remote control

Besides adding the board specific code, this patch moves
the RC5 decoding code from bt8xx to ir-functions.c to make it available 
for all drivers.

Signed-off-by: Marc Fargas <telenieko.telenieko.com>
Signed-off-by: Hermann Pitton <hermann-pitton@arcor.de>
Signed-off-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>