mei: bus: Call bus routines from the core code

Register the MEI bus type against the kernel core bus APIs and
call the bus Rx handler from interrupt.c

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>