[IA64] evtchn_callback fix and clean

[IA64] evtchn_callback fix and clean

Since we had changed to use event callback to deliver interrupts,

1. The pending_interruption is changed to pending_event.

2. get_ivr, set_tpr, get_trp and set_eoi are not used or only used
   in the initialization phase. There is no need to write this code
   in assembly.  This code is deleted.

3. hyper_ssm_i needs to be rewritten to jump to entchn_callback_handler
   instead of iva+0x3000 interrupt handler.  I will do this later.

Signed-off-by: Anthony Xu  <anthony.xu@intel.com>