Input: iqs5xx - make reset GPIO optional

Input: iqs5xx - make reset GPIO optional

The device's hardware reset pin is only required if the platform
must be able to update the device's firmware.

As such, demote the reset GPIO to optional in support of devices
that ship with pre-programmed firmware and don't route the reset
pin back to the SoC.

In that case, the 'fw_file' attribute is hidden because there is
no way to open the bootloader. The logic is extended to the case
in which the device does not advertise bootloader support in the
first place.

Last but not least, remove the hardware reset performed at probe
because there is no reason to reset the device manually. A power
on reset function already ensures a clean reset at start-up.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20210323021006.367-1-jeff@labundy.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>