intel_mid: Added custom device_handler support

This patch provides a means to add custom handler for
SFI devices. If you set device_handler as NULL in
device_id table standard SFI device handler will be used.
If its not NULL custom handler will be called.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Link: http://lkml.kernel.org/r/1382049336-21316-8-git-send-email-david.a.cohen@linux.intel.com
Signed-off-by: David Cohen <david.a.cohen@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>