ALSA: usb-audio: Support changing input on Sound Blaster E1

The E1 has two headphone jacks, one of which can be set as a microphone
input. In the default mode, it uses the built-in microphone as an input.
By sending a special command, the second headphone jack is instead used
as an input.

This might work with the E3 as well, but I don't have one of those to
test it.

Signed-off-by: Ian Douglas Scott <ian@iandouglasscott.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>