mfd: cpcap-3mm5: Improve support for Apple 3 button headsets

mfd: cpcap-3mm5: Improve support for Apple 3 button headsets

Previously when an Apple 3 button headset was inserted, the driver would
report the MEDIA key as always pressed.  When the volume keys were pressed,
a release was reported, and when the key was actually released, a press
was reported again.

This patch improves Apple headset support by sending the MEDIA key
press and releases correctly based on whether the volume key is actually
pressed or released.  The 3 buttons are still treated the same due to
hardware limitations.

Change-Id: I8bcc59f95f40a8c98e3748d90e257ea1ec0eeaf5
Signed-off-by: Greg Meiste <w30289@motorola.com>