media: rc: imon: Allow iMON RC protocol for ffdc 7e device

[ Upstream commit b20a6e298bcb8cb8ae18de26baaf462a6418515b ]

Allow selecting the IR protocol, MCE or iMON, for a device that
identifies as follows (with config id 0x7e):

15c2:ffdc SoundGraph Inc. iMON PAD Remote Controller

As the driver is structured to default to iMON when both RC
protocols are supported, existing users of this device (using MCE
protocol) will need to manually switch to MCE (RC-6) protocol from
userspace (with ir-keytable, sysfs).

Signed-off-by: Darius Rad <alpha@area49.net>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>