V4L/DVB (8395): saa7134: Fix Kbuild dependency of ir-kbd-i2c

Currently, saa7134 is dependent of ir-kbd-i2c, since it uses a symbol that is
defined there. However, as this symbol is used only on saa7134, there's no
sense on keeping it defined there (or on ir-commons).

So, let's move it to saa7134 and remove one symbol for being exported.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>