[media] em28xx: initialize button/I2C IR earlier

The em28xx-input is used by 3 different types of input devices:
	- devices with buttons (like cameras and grabber devices);
	- devices with I2C remotes;
	- em2860 or latter chips with RC support embedded.
When the device has an I2C remote, all it needs to do is to call
the proper I2C driver (ir-i2c-kbd), passing the proper data to
it, and just leave the code.
Also, button devices have its own init code that doesn't depend on
having an IR or not (as a general rule, they don't have).
So, move its init code to fix bugs introduced by earlier patches
that prevent them to work.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>